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North Atlantic hotspot-ridge interaction near Jan Mayen Island

L.J. Elkins1,2,

1Department of Geology, Bryn Mawr College, 101 North Merion Avenue, Bryn Mawr, Pennsylvania 19010, USA
2Department of Earth and Atmospheric Sciences, University of Nebraska Lincoln, Lincoln, NE 68588, USA

C. Hamelin3,

3Center for Geobiology, University of Bergen, Allegaten 41 5007, Bergen, Norway

J. Blichert-Toft4,

4Laboratoire de Géologie de Lyon, Ecole Normale Superieure de Lyon, 46 Allée d’Italie, 69007 Lyon, France

S.R. Scott5,

5Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA

K.W.W. Sims5,

5Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA

I.A. Yeo6,

6GEOMAR, Helmholtz Center for Ocean Research Kiel, Wischhofstraße 1-3 24148, Kiel, Germany


C.W. Devey6,

6GEOMAR, Helmholtz Center for Ocean Research Kiel, Wischhofstraße 1-3 24148, Kiel, Germany

R.B. Pedersen3

3Center for Geobiology, University of Bergen, Allegaten 41 5007, Bergen, Norway

Affiliations  |  Corresponding Author  |  Cite as

Elkins, L.J., Hamelin, C., Blichert-Toft, J., Scott, S.R., Sims, K.W.W., Yeo, I.A., Devey, C.W., Pedersen, R.B. (2016) North Atlantic hotspot-ridge interaction near Jan Mayen Island. Geochem. Persp. Let. 2, 55-67.

Geochemical Perspectives Letters v2, n1  |  doi: 10.7185/geochemlet.1606
Received 17 August 2015  |  Accepted 21 December 2015  |  Published 22 January 2016
Copyright © 2016 European Association of Geochemistry

Keywords: mid-ocean ridge, lead, strontium, neodymium, radiogenic isotopes, Jan Mayen, Kolbeinsey Ridge, Mohns Ridge, hotspot, hotspot-ridge interaction



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Abstract


At slow to ultraslow spreading rates along mid-ocean ridges, thicker lithosphere typically impedes magma generation and tectonic extension can play a more significant role in crustal production (Dick et al., 2003

Dick, H.J.B., Lin, J., Schouten, H. (2003) An ultraslow-spreading class of ocean ridge. Nature 426, 405-412.

). The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984

Neumann, E.R., Schilling, J.G. (1984) Petrology of Basalts from the Mohns-Knipovich Ridge - the Norwegian-Greenland Sea. Contributions to Mineralogy and Petrology 85, 209-223.

; Mertz et al., 1991

Mertz, D.F., Devey, C.W., Todt, W., Stoffers, P., Hofmann, A.W. (1991) Sr-Nd-Pb Isotope Evidence against Plume Asthenosphere Mixing North of Iceland. Earth and Planetary Science Letters 107, 243-255.

; Haase et al., 1996

Haase, K.M., Devey, C.W., Mertz, D.F., Stoffers, P., Garbe-Schönberg, D. (1996) Geochemistry of lavas from Mohns ridge, Norwegian-Greenland Sea: Implications for melting conditions and magma sources near Jan Mayen. Contributions to Mineralogy and Petrology 123, 223-237.

; Schilling et al., 1999

Schilling, J.G., Kingsley, R., Fontignie, D., Poreda, R., Xue, S. (1999) Dispersion of the Jan Mayen and Iceland mantle plumes in the Arctic: A He-Pb-Nd-Sr isotope tracer study of basalts from the Kolbeinsey, Mohns, and Knipovich Ridges. Journal of Geophysical Research-Solid Earth 104, 10543-10569.

; Trønnes et al., 1999

Trønnes, R.G., Planke, S., Sundvoll, B., Imsland, P. (1999) Recent volcanic rocks from Jan Mayen: Low-degree melt fractions of enriched northeast Atlantic mantle. Journal of Geophysical Research-Solid Earth 104, 7153-7168.

; Haase et al., 2003

Haase, K.M., Devey, C.W., Wieneke, M. (2003) Magmatic processes and mantle heterogeneity beneath the slow-spreading northern Kolbeinsey Ridge segment, North Atlantic. Contributions to Mineralogy and Petrology 144, 428-448.

; Mertz et al., 2004

Mertz, D.F., Sharp, W.D., Haase, K.M. (2004) Volcanism on the Eggvin Bank (Central Norwegian-Greenland Sea, latitude similar to 71 degrees N): age, source, and relationship to the Iceland and putative Jan Mayen plumes. Journal of Geodynamics 38, 57-83.

; Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

; Debaille et al., 2009

Debaille, V., Trønnes, R.G., Brandon, A.D., Waight, T.E., Graham, D.W., Lee, C.-T.A. (2009) Primitive off-rift basalts from Iceland and Jan Mayen: Os-isotopic evidence for a mantle source containing enriched subcontinental lithosphere. Geochimica et Cosmochimica Acta 73, 3423-3449.

). Here we show that Jan Mayen volcanism is likely the surface expression of a small mantle plume, which exerts significant influence on nearby mid-ocean ridge tectonics and volcanism. Progressive dilution of Jan Mayen geochemical signatures with distance from the hotspot is observed in lava samples from the immediately adjacent Mohns Ridge, and morphological indicators of enhanced magma supply are observed on both the Mohns Ridge and the nearby Kolbeinsey Ridge, which additionally locally overlies a highly heterogeneous, eclogite-bearing mantle source. These morphological and geochemical influences underscore the importance of heterogeneous mantle sources in modifying melt supply and thus the local expression of tectonic boundaries.

Figures and Tables

Figure 1 (a) Multibeam bathymetric map of the NKR, showing the Eggvin Bank and numbered dredge locations for samples analysed in this study. (b) Regional bathymetric map showing distribution of labelled seafloor features and Jan Mayen Island, with sample locations for this study from Jan Mayen Island (red), NKR (colours as in panel a), and SMR (orange). (c) Map with highlighted areas showing the proposed zones of underlying mantle melt generation and migration (blue: Kolbeinsey-type; purple: Eggvin-type; orange: Mohns-type; and red circle: Jan Mayen-type mantle).

Table 1 Radiogenic isotope compositions measured by ICP-MS.*

Figure 2 (a) εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2). Curves show calculated binary mixing trajectories between hypothesised geochemical compositions for Jan Mayen- (red box), Mohns- (yellow), Kolbeinsey- (blue) and Eggvin- (green) type melt endmembers, where tickmarks show percentage contributions of a pure Jan Mayen- or Eggvin-derived magma to a mixture. The Jan Mayen endmember, based on the most extreme enriched measurements for the island (Tables 1, S-2) has εHf = +10.5, εNd = +4.7, 206Pb/204Pb = 18.85, 207Pb/204Pb = 15.517, and Hf, Nd, and Pb concentrations of 6.9, 38.7, and 3.7 ppm, respectively. The hypothesised Mohns endmember, extrapolated to values that best explain available SMR samples as binary mixtures of Jan Mayen-Mohns Ridge lavas, has εHf = +24, εNd = +10.1, 206Pb/204Pb = 17.9, 207Pb/204Pb = 15.41, and Hf, Nd, and Pb concentrations of 5.6, 30, and 0.7, ppm, respectively; this composition is reasonable compared to published measurements from the Mohns Ridge (Schilling et al., 1983; Schilling et al., 1999; Blichert-Toft et al., 2005; Elkins et al., 2014). The Kolbeinsey endmember, based on depleted values from a suite of published MKR measurements (Schilling et al., 1983; Blichert-Toft et al., 2005; Elkins et al., 2011) and NKR sample POS436 246DR-2, has εHf = +19.2, εNd = +10, 206Pb/204Pb = 18.0, 207Pb/204Pb = 15.43, and Hf, Nd, and Pb concentrations of 0.5, 3, and 0.3 ppm, respectively; mixtures of Jan Mayen and Kolbeinsey endmembers cannot fully explain NKR lava compositions. The Eggvin-type component was extrapolated to values that best explain NKR basalts as mixtures between Kolbeinsey and an unknown enriched component, with εHf = +11, εNd = +5, 206Pb/204Pb = 18.96, 207Pb/204Pb = 15.528, 208Pb/204Pb = 38.72, and Hf, Nd, and Pb concentrations of 3, 22, and 11 ppm. Note that the high Pb content of the Eggvin-type endmember is necessary to generate a sufficiently hyperbolic mixing trajectory to account for NKR basalts.

Figure 3 Geochemical indicators vs. along-axis distance for the NKR and SMR, with the position of Jan Mayen Island projected westward onto the NKR using a geographic contour that runs parallel to the Jan Mayen Fracture Zone. (a) (Sm/Yb), sensitive to the presence of garnet in, and the trace element makeup of, the source. The variation between Jan Mayen Island/SMR and the NKR likely reflects a heterogeneous mantle source. (b) αSm-Nd; because Sm is always more compatible than Nd during melting, values less than unity reflect the degree of melting of the model source, while values greater than unity (e.g., MKR basalts; Salters, 1996; Elkins et al., 2011) require a different source composition and/or younger age than recorded by radiogenic isotopes.

Figure 1 Table 1 Figure 2 Figure 3

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Supplementary Figures and Tables

Figure S-1 (a) Chondrite-normalised (McDonough and Sun, 1995) REE concentrations and (b) N-MORB (Hofmann, 1988) normalised trace element concentrations for samples from this study (Table S-2). NKR basalts have elevated Pb and HREE compared to Jan Mayen Island and the MKR, indicating that they cannot be simple mixtures of Kolbeinsey-type and Jan Mayen-type magmas. High (230Th/238U) ratios measured in NKR lavas also require the presence of garnet in the melt source, indicating that the trace element compositions in Eggvin Bank basalts is principally controlled by mantle source composition.

Figure S-2 εHf vs. 206Pb/204Pb for the Jan Mayen region, with symbols, mixing trajectories, and references as in Figure 2.

Figure S-3 (La/Sm) vs. FeO* for basalt samples from the Kolbeinsey Ridge and the NKR, using data from Haase et al. (2003) and C. Devey, M. Wieneke, and K. Haase (unpub. data). Linear best-fit regression for Kolbeinsey Ridge samples suggests a slight positive relationship between FeO* and (La/Sm)N, likely controlled by degree of melting. Basalt rocks from the NKR are restricted to generally higher (La/Sm)N and lower FeO* values than the rest of the Kolbeinsey Ridge, best explained by an eclogite-bearing, incompatible element-enriched mantle source beneath the Eggvin Bank.

Figure S-4 (a) 87Sr/86Sr vs. Pb, and (b) εNd vs. Pb. for the Jan Mayen region, with symbols and references as in Figure 2. The data support lithologically and isotopically heterogeneous mantle source compositions for the Jan Mayen region and corroborate the existence of an Eggvin Bank end-member distinct from Jan Mayen mantle.

Figure S-1 Figure S-2 Figure S-3 Figure S-4

Table S-1 Location information for new submarine samples analyzed in this study.

Table S-2 Trace element abundance measured by ICP-MS.

Table S-3 Major element composition results.

Table S-1 Table S-2 Table S-3

View all supplementary figures and tables  


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Letter


The normal accretion process along divergent plate boundaries can be notably altered in hotspot-ridge interaction settings, where elevated mantle temperature anomalies enhance mantle melting, generating unusually thick oceanic crust (e.g., Schilling et al., 1985

Schilling, J.G., Thompson, G., Kingsley, R., Humphris, S. (1985) Hotspot-migrating ridge interaction in the South Atlantic. Nature 313, 187-191.

; Schilling, 1991

Schilling, J.G. (1991) Fluxes and excess temperatures of mantle plumes inferred from their interaction with migrating mid-ocean ridges. Nature 352, 397-403.

; Gale et al., 2013

Gale, A., Dalton, C.A., Langmuir, C.H., Su, Y., Schilling, J.G. (2013) The mean composition of ocean ridge basalts. Geochemistry Geophysics Geosystems 14, 489-518.

, 2014

Gale, A., Langmuir, C.H., Dalton, C.A. (2014) The global systematics of ocean ridge basalts and their origin. Journal of Petrology 55, 1051-1082.

). Jan Mayen and its immediate environs in the North Atlantic (Fig. 1) include an intraplate, volcanically-active island or hotspot (Jan Mayen Island), positioned at the northern terminus of a small, rifted microcontinent (Jan Mayen Ridge; Johnson and Heezen, 1967

Johnson, G.L., Heezen, B.C. (1967) Arctic Mid-Oceanic Ridge. Nature 215, 724-728.

; Kodaira et al., 1997

Kodaira, S., Mjelde, R., Gunnarsson, K., Shiobara, H., Shimamura, H. (1997) Crustal structure of the Kolbeinsey Ridge, North Atlantic, obtained by use of ocean bottom seismographs. Journal of Geophysical Research-Solid Earth 102, 3131-3151.

; Gaina et al., 2009

Gaina, C., Gernigon, L., Ball, P. (2009) Palaeocene-Recent plate boundaries in the NE Atlantic and the formation of the Jan Mayen microcontinent. Journal of the Geological Society of London 166, 601-616.

) and adjacent to two second-order ultraslow-spreading (Dick et al., 2003

Dick, H.J.B., Lin, J., Schouten, H. (2003) An ultraslow-spreading class of ocean ridge. Nature 426, 405-412.

) ridge segments, the Northern Kolbeinsey Ridge (NKR) and Southern Mohns Ridge (SMR), and the Jan Mayen Fracture Zone, a major fracture zone with ~200 km of transform offset. Although different in key ways, broad geochemical similarities between Jan Mayen Island and Icelandic lavas have suggested the influence of a mantle plume (either a unique Jan Mayen plume or emplaced Icelandic material) on mantle melting beneath Jan Mayen Island (Schilling et al., 1999

Schilling, J.G., Kingsley, R., Fontignie, D., Poreda, R., Xue, S. (1999) Dispersion of the Jan Mayen and Iceland mantle plumes in the Arctic: A He-Pb-Nd-Sr isotope tracer study of basalts from the Kolbeinsey, Mohns, and Knipovich Ridges. Journal of Geophysical Research-Solid Earth 104, 10543-10569.

; Trønnes et al., 1999

Trønnes, R.G., Planke, S., Sundvoll, B., Imsland, P. (1999) Recent volcanic rocks from Jan Mayen: Low-degree melt fractions of enriched northeast Atlantic mantle. Journal of Geophysical Research-Solid Earth 104, 7153-7168.

; Debaille et al., 2009

Debaille, V., Trønnes, R.G., Brandon, A.D., Waight, T.E., Graham, D.W., Lee, C.-T.A. (2009) Primitive off-rift basalts from Iceland and Jan Mayen: Os-isotopic evidence for a mantle source containing enriched subcontinental lithosphere. Geochimica et Cosmochimica Acta 73, 3423-3449.

). The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen’s high magma production rate and enriched chemistry (Imsland, 1986

Imsland, P. (1986) The volcanic eruption on Jan Mayen, January 1985: Interaction between a volcanic island and a fracture zone. Journal of Volcanology and Geothermal Research 28, 45-53.

; Maaløe et al., 1986

Maaløe, S., Sørensen, I. B., Hertogen, J. (1986) The trachybasaltic suite of Jan Mayen. Journal of Petrology 27, 439-466.

; Thy et al., 1991

Thy, P., Lofgren, G.E., Imsland, P. (1991) Melting relations and the evolution of the Jan Mayen magma system. Journal of Petrology 32, 303-332.

): cold edge effects near the fracture zone (Mertz et al., 1991

Mertz, D.F., Devey, C.W., Todt, W., Stoffers, P., Hofmann, A.W. (1991) Sr-Nd-Pb Isotope Evidence against Plume Asthenosphere Mixing North of Iceland. Earth and Planetary Science Letters 107, 243-255.

; Haase et al., 1996

Haase, K.M., Devey, C.W., Mertz, D.F., Stoffers, P., Garbe-Schönberg, D. (1996) Geochemistry of lavas from Mohns ridge, Norwegian-Greenland Sea: Implications for melting conditions and magma sources near Jan Mayen. Contributions to Mineralogy and Petrology 123, 223-237.

), variably melting source heterogeneities (Mertz et al., 1991

Mertz, D.F., Devey, C.W., Todt, W., Stoffers, P., Hofmann, A.W. (1991) Sr-Nd-Pb Isotope Evidence against Plume Asthenosphere Mixing North of Iceland. Earth and Planetary Science Letters 107, 243-255.

; Haase et al., 2003

Haase, K.M., Devey, C.W., Wieneke, M. (2003) Magmatic processes and mantle heterogeneity beneath the slow-spreading northern Kolbeinsey Ridge segment, North Atlantic. Contributions to Mineralogy and Petrology 144, 428-448.

; Mertz et al., 2004

Mertz, D.F., Sharp, W.D., Haase, K.M. (2004) Volcanism on the Eggvin Bank (Central Norwegian-Greenland Sea, latitude similar to 71 degrees N): age, source, and relationship to the Iceland and putative Jan Mayen plumes. Journal of Geodynamics 38, 57-83.

), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

), or a locally wet mantle (Haase et al., 2003

Haase, K.M., Devey, C.W., Wieneke, M. (2003) Magmatic processes and mantle heterogeneity beneath the slow-spreading northern Kolbeinsey Ridge segment, North Atlantic. Contributions to Mineralogy and Petrology 144, 428-448.

; Mertz et al., 2004

Mertz, D.F., Sharp, W.D., Haase, K.M. (2004) Volcanism on the Eggvin Bank (Central Norwegian-Greenland Sea, latitude similar to 71 degrees N): age, source, and relationship to the Iceland and putative Jan Mayen plumes. Journal of Geodynamics 38, 57-83.

). Jan Mayen thus presents a useful case study for 1) exploring the mechanisms by which hotspot volcanism can influence ultraslow-spreading ridge morphology, behaviour, and volcanism, 2) determining the relationships between hotspot volcanism and ambient variations in mantle geochemistry, and 3) exploring the disputed origins of local volcanic activity.

For this study, we present comprehensive geochemical analyses (major and trace element concentrations and 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb compositions) for a suite of submarine volcanic rocks from the NKR, the SMR, and Jan Mayen Island (Tables 1, S-1, S-2, S-3). These geochemical results are interpreted in the context of an enhanced geologic perspective, thanks to new high-resolution bathymetry of the volcanic and tectonic submarine morphology (Fig. 1). All submarine samples were retrieved during recent research cruises in combination with new multibeam bathymetry (Pedersen et al., 2010

Pedersen, R.B., Thorseth, I.H., Nygård, T.E., Lilley, M.D., Kelley, D.S. (2010) Hydrothermal activity at the Arctic mid-ocean ridges. In: Rona, P.A., Devey, C.W., Dyment, J., Murton, B.J. (Eds.) Diversity of Hydrothermal Systems on Slow Spreading Ocean Ridges. AGU, 67-89.

; Devey, 2012

Devey, C. (2012) RV Poseidon Cruise Report 436 [POS436]: North Kolbeinsey Ridge - geochemistry and volcanology, 06.07.2012 (Kiel) - 31.07.2012 (Akureyri). GEOMAR, Kiel, Germany, doi: 10.3289/CR_POS_436.

). Three additional, subaerial alkali basalts from Jan Mayen Island are included for literature comparison (Maaløe et al., 1986

Maaløe, S., Sørensen, I. B., Hertogen, J. (1986) The trachybasaltic suite of Jan Mayen. Journal of Petrology 27, 439-466.

).


Figure 1 (a) Multibeam bathymetric map of the NKR, showing the Eggvin Bank and numbered dredge locations for samples analysed in this study. (b) Regional bathymetric map showing distribution of labelled seafloor features and Jan Mayen Island, with sample locations for this study from Jan Mayen Island (red), NKR (colours as in panel a), and SMR (orange). (c) Map with highlighted areas showing the proposed zones of underlying mantle melt generation and migration (blue: Kolbeinsey-type; purple: Eggvin-type; orange: Mohns-type; and red circle: Jan Mayen-type mantle).
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Table 1 Radiogenic isotope compositions measured by ICP-MS.*
SampleLocation**87Sr/86Sr176Hf/177Hf143Nd/144Nd206Pb/204Pb207Pb/204Pb208Pb/204Pb
Submarine samples:
POS436 242DR-2baNKR0.703151(5)0.283175(5)0.513006(6)18.892615.509338.6157
POS436 246DR-2aNKR0.702961(6)0.283255(4)0.513083(5)18.455315.454738.0857
POS436 235DR-1aaNKR0.703187(5)0.283177(4)0.513008(5)18.875615.517738.5990
POS436 253DR-E2aNKR0.703195(7)0.283175(4)0.513015(5)18.889915.521138.6184
POS436 253DR-6aNKR0.703203(7)0.283183(4)0.513019(5)18.888115.518538.6109
POS436 232DR-1aNKR0.703047(7)0.283217(4)0.513044(5)18.788115.500438.4908
POS436 209DR-2aaNKR0.703034(6)0.283231(4)0.513051(6)18.769915.500338.4689
POS436 222DR-1aNKR0.703040(7)0.283217(4)0.513043(6)18.815015.504738.5277
POS436 215DR-1aNKR0.703047(7)0.283203(4)0.513036(4)18.853815.511438.5652
SM01-DR-24-14bJM0.703368(8)-0.512910(5)18.833115.505738.5979
SM01-DR-23-3bJM0.703456(6)0.283088(7)0.512931(5)18.849415.507038.6082
SM01-DR-5-5bJM0.70343(8)0.283090(4)0.512914(5)18.814915.506138.5865
SM01-DR-60-43bJM0.703431(8)0.283083(4)0.512918(5)18.809515.505138.5795
SM01-DR-100-01bSMR0.703395(8)0.283233(5)0.512978(5)18.794615.497938.5077
CGB-2011-D17-2aaSMR0.703339(6)0.283265(4)0.512991(6)18.720615.494938.4695
SM01-DR70-1aSMR0.703391(5)0.283236(4)0.512979(5)18.740915.499538.4923
SM01-DR67-4bSMR0.703417(8)0.283196(4)0.512983(5)18.828515.501238.5407
SM01-DR-91-13bSMR-0.283314(5)----
Subaerial samples (samples from Maaløe et al., 1986

Maaløe, S., Sørensen, I. B., Hertogen, J. (1986) The trachybasaltic suite of Jan Mayen. Journal of Petrology 27, 439-466.

):
JM-192aJM0.703490(7)0.283083(4)0.512880(6)18.764815.516738.6121
JM-71aJM0.703454(6)0.283068(4)0.512901(5)18.818615.517038.6310
JM-84aJM0.703453(7)0.283087(4)0.512903(6)18.840415.509038.6229

* Values in parentheses indicate 2s uncertainty for the last digit expressed.
** NKR: Northern Kolbeinsey Ridge; JM: Jan Mayen Island; SMR: Southern Mohns Ridge.
a 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 176Hf/177Hf, and 143Nd/144Nd measured by MC-ICP-MS (Nu Plasma HR) at the Ecole Normale Supérieure de Lyon. Strontium isotopes were analyzed at the University of Wyoming by MC-ICP-MS (ThermoFinnigan NeptunePlus). See Supplementary

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In agreement with previous work (Trønnes et al., 1999

Trønnes, R.G., Planke, S., Sundvoll, B., Imsland, P. (1999) Recent volcanic rocks from Jan Mayen: Low-degree melt fractions of enriched northeast Atlantic mantle. Journal of Geophysical Research-Solid Earth 104, 7153-7168.

; Debaille et al., 2009

Debaille, V., Trønnes, R.G., Brandon, A.D., Waight, T.E., Graham, D.W., Lee, C.-T.A. (2009) Primitive off-rift basalts from Iceland and Jan Mayen: Os-isotopic evidence for a mantle source containing enriched subcontinental lithosphere. Geochimica et Cosmochimica Acta 73, 3423-3449.

), Jan Mayen Island lavas are “enriched” with relatively high 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb and low eHf and eNd (e.g., 87Sr/86Sr = 0.703368-0.703490) (Table 1), and with trace element abundances resembling other ocean island basalts (Table S-2, Fig. S-1). While similar, Jan Mayen area lavas exhibit a distinct geochemical composition from Icelandic lavas (e.g., higher 87Sr/86Sr and Pb isotope ratios, lower 143Nd/144Nd and 176Hf/177Hf, normal MORB 3He/4He, and distinct 187Os/188Os on Jan Mayen Island; Schilling et al., 1999

Schilling, J.G., Kingsley, R., Fontignie, D., Poreda, R., Xue, S. (1999) Dispersion of the Jan Mayen and Iceland mantle plumes in the Arctic: A He-Pb-Nd-Sr isotope tracer study of basalts from the Kolbeinsey, Mohns, and Knipovich Ridges. Journal of Geophysical Research-Solid Earth 104, 10543-10569.

; Hanan et al., 2000

Hanan, B.B., Blichert-Toft, J., Kingsley, R., Schilling, J.G. (2000) Depleted Iceland mantle plume geochemical signature: artifact of multicomponent mixing? Geochemistry Geophysics Geosystems 1, doi: 10.1029/1999GC000009.

; Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

; Debaille et al., 2009

Debaille, V., Trønnes, R.G., Brandon, A.D., Waight, T.E., Graham, D.W., Lee, C.-T.A. (2009) Primitive off-rift basalts from Iceland and Jan Mayen: Os-isotopic evidence for a mantle source containing enriched subcontinental lithosphere. Geochimica et Cosmochimica Acta 73, 3423-3449.

), suggesting an enriched source discrete from the Icelandic hotspot source, possibly entraining subcontinental lithospheric mantle (SCLM) (Debaille et al., 2009

Debaille, V., Trønnes, R.G., Brandon, A.D., Waight, T.E., Graham, D.W., Lee, C.-T.A. (2009) Primitive off-rift basalts from Iceland and Jan Mayen: Os-isotopic evidence for a mantle source containing enriched subcontinental lithosphere. Geochimica et Cosmochimica Acta 73, 3423-3449.

). The submarine samples from Jan Mayen Island appear relatively evolved compared to the most magnesian subaerial samples of this study (MgO = 5.1-6.45 vs. 10.6-11.1 wt. %; Table S-3), but as previously observed, there are no systematic trace element or isotopic variations correlating with differentiation, arguing against detectable crustal assimilation (Trønnes et al., 1999

Trønnes, R.G., Planke, S., Sundvoll, B., Imsland, P. (1999) Recent volcanic rocks from Jan Mayen: Low-degree melt fractions of enriched northeast Atlantic mantle. Journal of Geophysical Research-Solid Earth 104, 7153-7168.

) (Tables 1, S-2, S-3).

The Mohns Ridge is an ultraslow-spreading ridge (17 mm yr-1 full-spreading rate; Mosar et al., 2002

Mosar, J., Lewis, G., Torsvik, T.H. (2002) North Atlantic sea-floor spreading rates: implications for the Tertiary development of inversion structures of the Norwegian-Greenland Sea. Journal of the Geological Society of London 159, 503-515.

; Dick et al., 2003

Dick, H.J.B., Lin, J., Schouten, H. (2003) An ultraslow-spreading class of ocean ridge. Nature 426, 405-412.

) north of Jan Mayen Island with relatively thin crust (~4 km; Klingelhofer et al., 2000

Klingelhofer, F., Géli, L., White, R.S. (2000) Geophysical and geochemical constraints on crustal accretion at the very-slow spreading Mohns Ridge. Geophysical Research Letters 27, 1547-1550.

; Okino et al., 2002

Okino, K., Curewitz, D., Asada, M., Tamaki, K., Vogt, P., Crane, K. (2002) Preliminary analysis of the Knipovich Ridge segmentation: influence of focused magmatism and ridge obliquity on an ultraslow spreading system. Earth and Planetary Science Letters 202, 275-288.

; Ljones et al., 2004

Ljones, F., Kuwano, A., Mjelde, R., Breivik, A., Shimamura, H., Murai, Y., Nishimura, Y. (2004) Crustal transect from the North Atlantic Knipovich Ridge to the Svalbard margin west of hornsund. Tectonophysics 378, 17-41.

; Kandilarov et al., 2008

Kandilarov, A., Mjelde, R., Okino, K., Murai, Y. (2008) Crustal structure of the ultra-slow spreading Knipovich Ridge, North Atlantic, along a presumed amagmatic portion of oceanic crustal formation. Marine Geophysical Researches 29, 109-134.

) and mainly characterised by highly oblique spreading expressed as a series of en echelon rift basins (Géli et al., 2012

Géli, L., Renard, V., Rommevaux, C. (2012) Ocean crust formation processes at very slow spreading centers: A model for the Mohns RIdge, near 72ºN, based on magnetic, gravity, and seismic data. Journal of Geophysical Research: Solid Earth 99, 2995-3013.

). In contrast, its southern segment (the SMR) has an orthogonal spreading direction and irregular off-axis crustal morphology, with a shallower ridge axis and thicker crust (~10 km; Kandilarov et al., 2012

Kandilarov, A., Mjelde, R., Pedersen, R.B., Hellevang, B., Papenberg, C., Petersen, C.J., Planert, L., Flueh, E. (2012) The northern boundary of the Jan Mayen microcontinent, North Atlantic determined from ocean bottom seismic, multichannel seismic, and gravity data. Marine Geophysical Research 33, 55-76.

) (Fig. 1). Recent mapping indicates the presence of large, partly eroded volcanic structures, often bisected by faulting (Pedersen et al., 2010

Pedersen, R.B., Thorseth, I.H., Nygård, T.E., Lilley, M.D., Kelley, D.S. (2010) Hydrothermal activity at the Arctic mid-ocean ridges. In: Rona, P.A., Devey, C.W., Dyment, J., Murton, B.J. (Eds.) Diversity of Hydrothermal Systems on Slow Spreading Ocean Ridges. AGU, 67-89.

). We interpret these structural and morphological characteristics as indicative of magma supply considerably higher than along the rest of the Mohns Ridge, possibly reflecting the influence of a nearby mantle plume associated with enhanced melt production.

Typical Mohns Ridge MORB are characterised by relatively high incompatible element contents and enriched radiogenic isotope values (Schilling et al., 1999

Schilling, J.G., Kingsley, R., Fontignie, D., Poreda, R., Xue, S. (1999) Dispersion of the Jan Mayen and Iceland mantle plumes in the Arctic: A He-Pb-Nd-Sr isotope tracer study of basalts from the Kolbeinsey, Mohns, and Knipovich Ridges. Journal of Geophysical Research-Solid Earth 104, 10543-10569.

; Elkins et al., 2014

Elkins, L.J., Sims, K.W.W., Prytulak, J., Blichert-Toft, J., Elliott, T., Blusztajn, J., Fretzdorff, S., Reagan, M., Haase, K., Humphris, S., Schilling, J.G. (2014) Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges. Geochimica et Cosmochimica Acta 127, 140-170.

), but with relatively high 208Pb/204Pb and 207Pb/204Pb for a given 206Pb/204Pb, akin to the so-called DUPAL anomaly observed in the southern oceans (Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

). The lavas are further characterised by unusually high εHf for a given εNd (Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

), best explained by ancient garnet in the mantle source, perhaps hosted by SCLM. Such a source could have originated as delaminated Greenland continental lithosphere during rifting of the relatively young Greenland basin. All SMR basaltic glasses analysed here are tholeiitic with geochemistry intermediate between typical Mohns Ridge MORB and lavas from Jan Mayen Island, readily explained as products of straightforward binary mixing between Mohns Ridge-type and Jan Mayen Island-type endmember magmas (Figs. 2, 3, S-1, S-2, Table 1).


Figure 2 (a) εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975

Sun, S.S., Jahn, B. (1975) Lead and Strontium Isotopes in Postglacial Basalts from Iceland. Nature 255, 527-530.

; Zindler et al., 1979

Zindler, A., Hart, S.R., Frey, F.A. (1979) Nd and Sr isotope ratios and rare earth element abundances in Reykjanes Peninsula basalts evidence for mantle heterogeneity beneath Iceland. Earth and Planetary Science Letters 45, 249-262.

; Óskarsson et al., 1982

Óskarsson, N., Sigvaldason, G., Steinthorsson, S. (1982) A dynamic model of rift zone petrogenesis and the regional petrology of Iceland. Journal of Petrology 23, 28-74.

; Hemond et al., 1993

Hemond, C., Arndt, N.T., Lichtenstein, U., Hofmann, A.W., Oskarsson, N., Steinthorsson, S. (1993) The Heterogeneous Iceland Plume - Nd-Sr-O Isotopes and Trace-Element Constraints. Journal of Geophysical Research-Solid Earth 98, 15833-15850.

; Nowell et al., 1998

Nowell, G.M., Kempton, P.D., Noble, S.R., Fitton, J.G., Saunders, A.D., Mahoney, J.J., Taylor, R.N. (1998) High precision Hf isotope measurements of MORB and OIB by thermal ionisation mass spectrometry; insights into the depleted mantle. Chemical Geology 149, 211-233.

; Salters and White, 1998

Salters, V.J.M., White, W.M. (1998) Hf isotope constraints on mantle evolution. Chemical Geology 145, 447-460.

; Schilling et al., 1999

Schilling, J.G., Kingsley, R., Fontignie, D., Poreda, R., Xue, S. (1999) Dispersion of the Jan Mayen and Iceland mantle plumes in the Arctic: A He-Pb-Nd-Sr isotope tracer study of basalts from the Kolbeinsey, Mohns, and Knipovich Ridges. Journal of Geophysical Research-Solid Earth 104, 10543-10569.

; Chauvel and Hémond, 2000

Chauvel, C., Hémond, C. (2000) Melting of a complete section of recycled oceanic crust: Trace element and Pb isotopic evidence from Iceland. Geochemistry Geophysics Geosystems 1, 1001.

; Kempton et al., 2000

Kempton, P.D., Fitton, J.G., Saunders, A.D., Nowell, G.M., Taylor, R.N., Hardarson, B.S., Pearson, G. (2000) The Iceland plume in space and time: a Sr-Nd-Pb-Hf study of the North Atlantic rifted margin. Earth and Planetary Science Letters 177, 255-271.

; Stracke et al., 2003

Stracke, A., Zindler, A., Salters, V.J.M., McKenzie, D., Blichert-Toft, J., Albarède, F., Gronvold, K. (2003) Theistareykir revisited. Geochemistry Geophysics Geosystems 4, doi: 10.1029/2001gc000201.

; Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

; Elkins et al., 2011

Elkins, L.J., Sims, K.W.W., Prytulak, J., Mattielli, N., Elliott, T., Blichert-Toft, J., Blusztajn, J., Dunbar, N., Devey, C. W., Mertz, D.F., Schilling, J.G. (2011) Understanding melt generation beneath the slow spreading Kolbeinsey Ridge from 238U, 230Th, and 231Pa excesses. Geochimica et Cosmochimica Acta 75, 6300-6329.

; Sims et al., 2013

Sims, K.W.W., Maclennan, J., Blichert-Toft, J., Mervine, E. M., Blusztajn, J., Grönvold, K. (2013) Short length scale mantle heterogeneity beneath Iceland probed by glacial modulation of melting. Earth and Planetary Science Letters 379, 146-157.

; Elkins et al., 2014

Elkins, L.J., Sims, K.W.W., Prytulak, J., Blichert-Toft, J., Elliott, T., Blusztajn, J., Fretzdorff, S., Reagan, M., Haase, K., Humphris, S., Schilling, J.G. (2014) Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges. Geochimica et Cosmochimica Acta 127, 140-170.

) (Tables 1, S-2). Curves show calculated binary mixing trajectories between hypothesised geochemical compositions for Jan Mayen- (red box), Mohns- (yellow), Kolbeinsey- (blue) and Eggvin- (green) type melt endmembers, where tickmarks show percentage contributions of a pure Jan Mayen- or Eggvin-derived magma to a mixture. The Jan Mayen endmember, based on the most extreme enriched measurements for the island (Tables 1, S-2) has εHf = +10.5, εNd = +4.7, 206Pb/204Pb = 18.85, 207Pb/204Pb = 15.517, and Hf, Nd, and Pb concentrations of 6.9, 38.7, and 3.7 ppm, respectively. The hypothesised Mohns endmember, extrapolated to values that best explain available SMR samples as binary mixtures of Jan Mayen-Mohns Ridge lavas, has εHf = +24, εNd = +10.1, 206Pb/204Pb = 17.9, 207Pb/204Pb = 15.41, and Hf, Nd, and Pb concentrations of 5.6, 30, and 0.7, ppm, respectively; this composition is reasonable compared to published measurements from the Mohns Ridge (Schilling et al., 1983

Schilling, J.G., Zajac, M., Evans, R., Johnston, T., White, W., Devine, J.D., Kingsley, R. (1983) Petrologic and Geochemical Variations Along the Mid-Atlantic Ridge from 29-Degrees-N to 73-Degrees-N. American Journal of Science 283, 510-586.

; Schilling et al., 1999

Schilling, J.G., Kingsley, R., Fontignie, D., Poreda, R., Xue, S. (1999) Dispersion of the Jan Mayen and Iceland mantle plumes in the Arctic: A He-Pb-Nd-Sr isotope tracer study of basalts from the Kolbeinsey, Mohns, and Knipovich Ridges. Journal of Geophysical Research-Solid Earth 104, 10543-10569.

; Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

; Elkins et al., 2014

Elkins, L.J., Sims, K.W.W., Prytulak, J., Blichert-Toft, J., Elliott, T., Blusztajn, J., Fretzdorff, S., Reagan, M., Haase, K., Humphris, S., Schilling, J.G. (2014) Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges. Geochimica et Cosmochimica Acta 127, 140-170.

). The Kolbeinsey endmember, based on depleted values from a suite of published MKR measurements (Schilling et al., 1983

Schilling, J.G., Zajac, M., Evans, R., Johnston, T., White, W., Devine, J.D., Kingsley, R. (1983) Petrologic and Geochemical Variations Along the Mid-Atlantic Ridge from 29-Degrees-N to 73-Degrees-N. American Journal of Science 283, 510-586.

; Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

; Elkins et al., 2011

Elkins, L.J., Sims, K.W.W., Prytulak, J., Mattielli, N., Elliott, T., Blichert-Toft, J., Blusztajn, J., Dunbar, N., Devey, C. W., Mertz, D.F., Schilling, J.G. (2011) Understanding melt generation beneath the slow spreading Kolbeinsey Ridge from 238U, 230Th, and 231Pa excesses. Geochimica et Cosmochimica Acta 75, 6300-6329.

) and NKR sample POS436 246DR-2, has εHf = +19.2, εNd = +10, 206Pb/204Pb = 18.0, 207Pb/204Pb = 15.43, and Hf, Nd, and Pb concentrations of 0.5, 3, and 0.3 ppm, respectively; mixtures of Jan Mayen and Kolbeinsey endmembers cannot fully explain NKR lava compositions. The Eggvin-type component was extrapolated to values that best explain NKR basalts as mixtures between Kolbeinsey and an unknown enriched component, with εHf = +11, εNd = +5, 206Pb/204Pb = 18.96, 207Pb/204Pb = 15.528, 208Pb/204Pb = 38.72, and Hf, Nd, and Pb concentrations of 3, 22, and 11 ppm. Note that the high Pb content of the Eggvin-type endmember is necessary to generate a sufficiently hyperbolic mixing trajectory to account for NKR basalts.
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Unlike the Mohns Ridge, the Kolbeinsey Ridge is overall characterised by orthogonal spreading at ultraslow rates (18 mm yr-1; Mosar et al., 2002

Mosar, J., Lewis, G., Torsvik, T.H. (2002) North Atlantic sea-floor spreading rates: implications for the Tertiary development of inversion structures of the Norwegian-Greenland Sea. Journal of the Geological Society of London 159, 503-515.

; Dick et al., 2003

Dick, H.J.B., Lin, J., Schouten, H. (2003) An ultraslow-spreading class of ocean ridge. Nature 426, 405-412.

) and relatively thick ocean crust (7-10 km; Kodaira et al., 1997

Kodaira, S., Mjelde, R., Gunnarsson, K., Shiobara, H., Shimamura, H. (1997) Crustal structure of the Kolbeinsey Ridge, North Atlantic, obtained by use of ocean bottom seismographs. Journal of Geophysical Research-Solid Earth 102, 3131-3151.

). The NKR segment has a shallower ridge axis and therefore thicker crust than the neighbouring Middle Kolbeinsey Ridge (MKR). While ultraslow ridges are typically characterised by thin crust, tectonic spreading, and peridotite exposure, those features are not observed in the Jan Mayen region despite ultraslow full-spreading rates of 17-18 mm yr-1 (Mosar et al., 2002

Mosar, J., Lewis, G., Torsvik, T.H. (2002) North Atlantic sea-floor spreading rates: implications for the Tertiary development of inversion structures of the Norwegian-Greenland Sea. Journal of the Geological Society of London 159, 503-515.

). Recent bathymetric mapping reveals that the Eggvin Bank in the centre of the NKR, in addition to being anomalously shallow, hosts fresh volcanic deposits indicative of high magma supply (e.g., sheet flows vs. monogenetic cones, a nearly subaerial volcanic edifice constructed atop the eastern axial flank wall, and fresh popping rocks) compared to the ends of the segment (Fig. 1). The large seamount lacks fresh fault scarps, suggesting elevated volcanic activity to maintain its height and cover active axial faulting. Regional bathymetry (Smith and Sandwell, 1997

Smith, W.H.F., Sandwell, D.T. (1997) Global sea floor topography from satellite altimetry and ship depth soundings. Science 277, 1956-1962.

) demonstrates the presence off-axis of shallow seafloor and highly segmented slopes persisting up to 30 km (~3 Ma) off-axis, further supporting a long-lived source of active volcanism. Bathymetry further reveals two parallel axial valleys to the south that both host fresh basalt (Fig. 1). This doubling of ridge axes suggests the segment is immature and can be explained by either active relocation of the segment towards the main, more easterly neovolcanic zone, or by simultaneously active, paired axial valleys as observed in Iceland. Either scenario suggests that NKR axial position is influenced by a long-lived source of enhanced magma supply.

Kolbeinsey Ridge basalts overall have notable depletions in incompatible trace elements and long-lived radiogenic isotope signatures, with high (230Th/238U) activity ratios, together suggesting high degrees of melting of a depleted garnet peridotite source (Elkins et al., 2014

Elkins, L.J., Sims, K.W.W., Prytulak, J., Blichert-Toft, J., Elliott, T., Blusztajn, J., Fretzdorff, S., Reagan, M., Haase, K., Humphris, S., Schilling, J.G. (2014) Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges. Geochimica et Cosmochimica Acta 127, 140-170.

). The abrupt change in purported mantle composition across the Jan Mayen Fracture Zone has been interpreted to indicate a sharp chemical discontinuity, perhaps reflecting a major mantle flow boundary (Haase et al., 1996

Haase, K.M., Devey, C.W., Mertz, D.F., Stoffers, P., Garbe-Schönberg, D. (1996) Geochemistry of lavas from Mohns ridge, Norwegian-Greenland Sea: Implications for melting conditions and magma sources near Jan Mayen. Contributions to Mineralogy and Petrology 123, 223-237.

) (Fig. 3). Former work identified more enriched isotopic and trace element signatures on the Eggvin Bank and NKR than the MKR, generally attributed to the influence of the Jan Mayen hotspot (Schilling et al., 1999

Schilling, J.G., Kingsley, R., Fontignie, D., Poreda, R., Xue, S. (1999) Dispersion of the Jan Mayen and Iceland mantle plumes in the Arctic: A He-Pb-Nd-Sr isotope tracer study of basalts from the Kolbeinsey, Mohns, and Knipovich Ridges. Journal of Geophysical Research-Solid Earth 104, 10543-10569.

; Haase et al., 2003

Haase, K.M., Devey, C.W., Wieneke, M. (2003) Magmatic processes and mantle heterogeneity beneath the slow-spreading northern Kolbeinsey Ridge segment, North Atlantic. Contributions to Mineralogy and Petrology 144, 428-448.

; Mertz et al., 2004

Mertz, D.F., Sharp, W.D., Haase, K.M. (2004) Volcanism on the Eggvin Bank (Central Norwegian-Greenland Sea, latitude similar to 71 degrees N): age, source, and relationship to the Iceland and putative Jan Mayen plumes. Journal of Geodynamics 38, 57-83.

; Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

). Likewise, NKR αSm-Nd values (where αSm-Nd = (Sm/Nd)sample / (Sm/Nd)source, and (Sm/Nd)source is calculated from 143Nd/144Ndsample using a mantle model age of 1.8 Ga; DePaolo, 1988

DePaolo, D. (1988) Neodymium isotope geochemistry: An introduction.

; Sims et al., 1995

Sims, K.W.W., Depaolo, D.J., Murrell, M.T., Baldridge, W.S., Goldstein, S.J., Clague, D.A. (1995) Mechanisms of Magma Generation beneath Hawaii and Midocean Ridges - Uranium/Thorium and Samarium/Neodymium Isotopic Evidence. Science 267, 508-512.

; Salters, 1996

Salters, V.J.M. (1996) The generation of mid-ocean ridge basalts from the Hf and Nd isotope perspective. Earth and Planetary Science Letters 141, 109-123.

) are more typical of global MORB (<1.0), unlike other Kolbeinsey Ridge basalts with αSm-Nd > 1.0 (Salters, 1996

Salters, V.J.M. (1996) The generation of mid-ocean ridge basalts from the Hf and Nd isotope perspective. Earth and Planetary Science Letters 141, 109-123.

; Elkins et al., 2011

Elkins, L.J., Sims, K.W.W., Prytulak, J., Mattielli, N., Elliott, T., Blichert-Toft, J., Blusztajn, J., Dunbar, N., Devey, C. W., Mertz, D.F., Schilling, J.G. (2011) Understanding melt generation beneath the slow spreading Kolbeinsey Ridge from 238U, 230Th, and 231Pa excesses. Geochimica et Cosmochimica Acta 75, 6300-6329.

), supporting a distinct mantle source beneath the NKR. While high (230Th/238U) activity ratios have suggested melting of a depleted garnet peridotite source for the MKR, NKR lavas have low (231Pa/235U) activity ratios, likely the product of rapid melting of garnet-bearing eclogite (Elkins et al., 2011

Elkins, L.J., Sims, K.W.W., Prytulak, J., Mattielli, N., Elliott, T., Blichert-Toft, J., Blusztajn, J., Dunbar, N., Devey, C. W., Mertz, D.F., Schilling, J.G. (2011) Understanding melt generation beneath the slow spreading Kolbeinsey Ridge from 238U, 230Th, and 231Pa excesses. Geochimica et Cosmochimica Acta 75, 6300-6329.

, 2014

Elkins, L.J., Sims, K.W.W., Prytulak, J., Blichert-Toft, J., Elliott, T., Blusztajn, J., Fretzdorff, S., Reagan, M., Haase, K., Humphris, S., Schilling, J.G. (2014) Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges. Geochimica et Cosmochimica Acta 127, 140-170.

). We note that the basalt from the eastern axial valley resembles other NKR lavas, including geochemical indicators of enrichment, while the western axial valley basalt more closely resembles MKR basalts and presumably does not sample the enriched mantle component beneath the Eggvin Bank (Figs. 2, 3, S-1, S-2).


Figure 3 Geochemical indicators vs. along-axis distance for the NKR and SMR, with the position of Jan Mayen Island projected westward onto the NKR using a geographic contour that runs parallel to the Jan Mayen Fracture Zone. (a) (Sm/Yb), sensitive to the presence of garnet in, and the trace element makeup of, the source. The variation between Jan Mayen Island/SMR and the NKR likely reflects a heterogeneous mantle source. (b) αSm-Nd; because Sm is always more compatible than Nd during melting, values less than unity reflect the degree of melting of the model source, while values greater than unity (e.g., MKR basalts; Salters, 1996

Salters, V.J.M. (1996) The generation of mid-ocean ridge basalts from the Hf and Nd isotope perspective. Earth and Planetary Science Letters 141, 109-123.

; Elkins et al., 2011

Elkins, L.J., Sims, K.W.W., Prytulak, J., Mattielli, N., Elliott, T., Blichert-Toft, J., Blusztajn, J., Dunbar, N., Devey, C. W., Mertz, D.F., Schilling, J.G. (2011) Understanding melt generation beneath the slow spreading Kolbeinsey Ridge from 238U, 230Th, and 231Pa excesses. Geochimica et Cosmochimica Acta 75, 6300-6329.

) require a different source composition and/or younger age than recorded by radiogenic isotopes.
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While the above observations may suggest plume influence on NKR basalt production, the composition of the enriched endmember in the NKR/Eggvin mantle source differs notably from the Jan Mayen mantle component inferred from Jan Mayen Island- and SMR-derived lavas (Fig. 2). For example, the more enriched basalts collected from the Eggvin Bank exhibit lower (Sm/Yb)N ratios than the Jan Mayen endmember (Table S-2, Figs. 3, S-1), which cannot be explained by a lack of residual garnet in the source, since NKR magmas are known to be products of melting in the presence of garnet from 230Th/238U > 1 (Elkins et al., 2011

Elkins, L.J., Sims, K.W.W., Prytulak, J., Mattielli, N., Elliott, T., Blichert-Toft, J., Blusztajn, J., Dunbar, N., Devey, C. W., Mertz, D.F., Schilling, J.G. (2011) Understanding melt generation beneath the slow spreading Kolbeinsey Ridge from 238U, 230Th, and 231Pa excesses. Geochimica et Cosmochimica Acta 75, 6300-6329.

, 2014

Elkins, L.J., Sims, K.W.W., Prytulak, J., Blichert-Toft, J., Elliott, T., Blusztajn, J., Fretzdorff, S., Reagan, M., Haase, K., Humphris, S., Schilling, J.G. (2014) Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges. Geochimica et Cosmochimica Acta 127, 140-170.

). Observed NKR trace element patterns thus likely reflect the composition of a distinct mantle source located beneath the Eggvin Bank. Although not as pronounced as DUPAL-type signatures to the north, this Eggvin-type mantle source also exhibits slightly elevated 207Pb/204Pb and 208Pb/204Pb ratios for a given 206Pb/204Pb and higher eHf for a given eNd (Table 1, Figs. 2, S-2). Moreover, if generated by binary mixing, the isotopic compositions of Eggvin Bank basalts require a notably Pb-rich Eggvin endmember magma (Fig. 2). In addition to the 231Pa/235U evidence for eclogite (Elkins et al., 2014

Elkins, L.J., Sims, K.W.W., Prytulak, J., Blichert-Toft, J., Elliott, T., Blusztajn, J., Fretzdorff, S., Reagan, M., Haase, K., Humphris, S., Schilling, J.G. (2014) Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges. Geochimica et Cosmochimica Acta 127, 140-170.

), partition coefficients for Pb, Si, Al, and Fe in eclogite support an eclogite-rich source contributing magmas with the relatively high Pb and SiO2 and low FeO and Al2O3 observed in NKR MORB (Haase et al., 2003

Haase, K.M., Devey, C.W., Wieneke, M. (2003) Magmatic processes and mantle heterogeneity beneath the slow-spreading northern Kolbeinsey Ridge segment, North Atlantic. Contributions to Mineralogy and Petrology 144, 428-448.

; Pertermann and Hirschmann, 2003

Pertermann, M., Hirschmann, M. (2003) Partial melting experiments on MORB-like pyroxenite between 2 and 3 GPa: Constraints on the presence of pyroxenite in basalt source regions from solidus location and melting rate. Journal of Geophysical Research 108, doi: 10.1029/2000JB000118.

) (Tables S-2, S-3, Figs. S-2, S-3, S-4). Such an eclogite-bearing source is supported by correlations between Pb and radiogenic isotopes, with higher Pb contents associated with the most enriched isotopic signatures for the NKR (Fig. S-4). We thus infer that the most likely mantle source for the Eggvin-type signature in NKR basalts is an eclogite-rich mantle containing ancient, high-eHf garnet (Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

). Existing models suggest that garnet-bearing veins or blobs of SCLM are present in the North Atlantic mantle, likely having originated under Greenland prior to basin rifting by delamination (Blichert-Toft et al., 2005

Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.

); a concentrated pocket of such material may plausibly have been trapped beneath the NKR by the relocation of the active ridge axis to the Kolbeinsey Ridge from the Aegir Ridge at ~25 Ma (Fig. 1). While the more fusible eclogite can generate thickened crust without elevated mantle temperatures, the other morphological evidence (large near-axis seamounts and paired axial valleys) and extreme nature of the crustal thickening would also support the influence of a plume on mantle temperature beneath the NKR.

Jan Mayen and environs demonstrate the dramatic extent to which magmatism generated by heterogeneous mantle, possibly with a plume source, can influence the structure and behaviour of ultraslow mid-ocean ridges. Here, multiple mantle heterogeneities within a relatively small geographic area have significantly modified the accretionary process of two ridge segments, generating enhanced magmatic activity, variations in spreading direction, adjusted axial locations, and, where mantle flow permits, the direct addition of heterogeneous, possibly plume-derived magma. We hence assert that the distinct morphology and tectonically-dominated accretionary style typical of ultraslow spreading ridges (Dick et al., 2003

Dick, H.J.B., Lin, J., Schouten, H. (2003) An ultraslow-spreading class of ocean ridge. Nature 426, 405-412.

) is particularly sensitive to even modest increases in mantle temperature and magma supply, which cause the ridge to take on growth properties more typical of slow- or intermediate-spreading ridges. For comparison, the 17 ºS location on the East Pacific Rise is adjacent to a small hotspot but shows little geomorphological impact at fast spreading rates (Mahoney et al., 1994

Mahoney, J.J., Sinton, J.M., Kurz, M.D., Macdougall, J.D., Spencer, K.J., Lugmair, G.W. (1994) Isotope and trace element characteristics of a super-fast spreading ridge: East Pacific Rise, 13-23ºS. Earth and Planetary Science Letters 121, 173-193.

). This demonstrates that for ultraslow ridges, the control on accretionary mechanisms is principally magma supply, which is typically but, importantly, not solely controlled by spreading rate.

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Acknowledgements


L.J.E. and K.W.W.S. acknowledge the Ocean Sciences Section of the National Science Foundation for supporting USA geochemical work and travel for this project. Geochemical analyses and field work were supported by the Norwegian Research Council in Norway to C.H. and R.P., and by the French Agence Nationale de la Recherche (ANR-10-BLAN-0603 M&Ms — Mantle Melting — Measurements, Models, Mechanisms) to J.B.T. I.A.Y. was supported by an A.v. Humboldt Fellowship. Jan Mayen Island samples from the Maaløe collection were supplied by D. DePaolo. Analyses at Boston University were performed by T. Ireland. We thank N. Augustin, M. Deutschmann, T. Laurila, K. Meisenhelder, E. Rivers, M. Rothenbeck, F. van der Zwan, and I. Yeo for field assistance on the F.S. Poseidon expedition in 2012; N. Augustin, I. Yeo, K. Meisenhelder, and R. Davis for assistance with bathymetric data; and E. Rivers, R. Davis, K. Meisenhelder, R. Chernow, Y. Ronen, S.H. Dundas, O. Tumyr and P. Telouk for assistance in the laboratory.

Editor: Graham Pearson


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References


Blichert-Toft, J., Agranier, A., Andres, M., Kingsley, R., Schilling, J.G., Albarède, F. (2005) Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic. Geochemistry Geophysics Geosystems 6, doi: 10.1029/2004GC000788.
Show in context

The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984; Mertz et al., 1991; Haase et al., 1996; Schilling et al., 1999; Trønnes et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005; Debaille et al., 2009).
View in article
The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen’s high magma production rate and enriched chemistry (Imsland, 1986; Maaløe et al., 1986; Thy et al., 1991): cold edge effects near the fracture zone (Mertz et al., 1991; Haase et al., 1996), variably melting source heterogeneities (Mertz et al., 1991; Haase et al., 2003; Mertz et al., 2004), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005), or a locally wet mantle (Haase et al., 2003; Mertz et al., 2004).
View in article
While similar, Jan Mayen area lavas exhibit a distinct geochemical composition from Icelandic lavas (e.g., higher 87Sr/86Sr and Pb isotope ratios, lower 143Nd/144Nd and 176Hf/177Hf, normal MORB 3He/4He, and distinct 187Os/188Os on Jan Mayen Island; Schilling et al., 1999; Hanan et al., 2000; Blichert-Toft et al., 2005; Debaille et al., 2009), suggesting an enriched source discrete from the Icelandic hotspot source, possibly entraining subcontinental lithospheric mantle (SCLM) (Debaille et al., 2009).
View in article
Typical Mohns Ridge MORB are characterised by relatively high incompatible element contents and enriched radiogenic isotope values (Schilling et al., 1999; 2005; Elkins et al., 2014), but with relatively high 208Pb/204Pb and 207Pb/204Pb for a given 206Pb/204Pb, akin to the so-called DUPAL anomaly observed in the southern oceans (Blichert-Toft et al., 2005).
View in article
The lavas are further characterised by unusually high εHf for a given εNd (Blichert-Toft et al., 2005), best explained by ancient garnet in the mantle source, perhaps hosted by SCLM.
View in article
Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
View in article
Figure 2 [...] The hypothesised Mohns endmember, extrapolated to values that best explain available SMR samples as binary mixtures of Jan Mayen-Mohns Ridge lavas, has εHf = +24, εNd = +10.1, 206Pb/204Pb = 17.9, 207Pb/204Pb = 15.41, and Hf, Nd, and Pb concentrations of 5.6, 30, and 0.7, ppm, respectively; this composition is reasonable compared to published measurements from the Mohns Ridge (Schilling et al., 1983; Schilling et al., 1999; Blichert-Toft et al., 2005; Elkins et al., 2014).
View in article
Figure 2 [...] The Kolbeinsey endmember, based on depleted values from a suite of published MKR measurements (Schilling et al., 1983; Blichert-Toft et al., 2005; Elkins et al., 2011) and NKR sample POS436 246DR-2, has εHf = +19.2, εNd = +10, 206Pb/204Pb = 18.0, 207Pb/204Pb = 15.43, and Hf, Nd, and Pb concentrations of 0.5, 3, and 0.3 ppm, respectively; mixtures of Jan Mayen and Kolbeinsey endmembers cannot fully explain NKR lava compositions.
View in article
Former work identified more enriched isotopic and trace element signatures on the Eggvin Bank and NKR than the MKR, generally attributed to the influence of the Jan Mayen hotspot (Schilling et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005).
View in article
We thus infer that the most likely mantle source for the Eggvin-type signature in NKR basalts is an eclogite-rich mantle containing ancient, high-eHf garnet (Blichert-Toft et al., 2005). Existing models suggest that garnet-bearing veins or blobs of SCLM are present in the North Atlantic mantle, likely having originated under Greenland prior to basin rifting by delamination (Blichert-Toft et al., 2005); a concentrated pocket of such material may plausibly have been trapped beneath the NKR by the relocation of the active ridge axis to the Kolbeinsey Ridge from the Aegir Ridge at ~25 Ma (Fig. 1).
View in article


Chauvel, C., Hémond, C. (2000) Melting of a complete section of recycled oceanic crust: Trace element and Pb isotopic evidence from Iceland. Geochemistry Geophysics Geosystems 1, 1001.
Show in context

Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
View in article


Debaille, V., Trønnes, R.G., Brandon, A.D., Waight, T.E., Graham, D.W., Lee, C.-T.A. (2009) Primitive off-rift basalts from Iceland and Jan Mayen: Os-isotopic evidence for a mantle source containing enriched subcontinental lithosphere. Geochimica et Cosmochimica Acta 73, 3423-3449.
Show in context

The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984; Mertz et al., 1991; Haase et al., 1996; Schilling et al., 1999; Trønnes et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005; Debaille et al., 2009).
View in article
Although different in key ways, broad geochemical similarities between Jan Mayen Island and Icelandic lavas have suggested the influence of a mantle plume (either a unique Jan Mayen plume or emplaced Icelandic material) on mantle melting beneath Jan Mayen Island (Schilling et al., 1999; Trønnes et al., 1999; Debaille et al., 2009).
View in article
In agreement with previous work (Trønnes et al., 1999; Debaille et al., 2009), Jan Mayen Island lavas are “enriched” with relatively high 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb and low eHf and eNd (e.g., 87Sr/86Sr = 0.703368-0.703490) (Table 1), and with trace element abundances resembling other ocean island basalts (Table S-2, Fig. S-1).
View in article
While similar, Jan Mayen area lavas exhibit a distinct geochemical composition from Icelandic lavas (e.g., higher 87Sr/86Sr and Pb isotope ratios, lower 143Nd/144Nd and 176Hf/177Hf, normal MORB 3He/4He, and distinct 187Os/188Os on Jan Mayen Island; Schilling et al., 1999; Hanan et al., 2000; Blichert-Toft et al., 2005; Debaille et al., 2009), suggesting an enriched source discrete from the Icelandic hotspot source, possibly entraining subcontinental lithospheric mantle (SCLM) (Debaille et al., 2009).
View in article


DePaolo, D. (1988) Neodymium isotope geochemistry: An introduction.
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Likewise, NKR αSm-Nd values (where αSm-Nd = (Sm/Nd)sample / (Sm/Nd)source, and (Sm/Nd)source is calculated from 143Nd/144Ndsample using a mantle model age of 1.8 Ga; DePaolo, 1988; Sims et al., 1995; Salters, 1996) are more typical of global MORB (<1.0), unlike other Kolbeinsey Ridge basalts with αSm-Nd > 1.0 (Salters, 1996; Elkins et al., 2011), supporting a distinct mantle source beneath the NKR.
View in article


Devey, C. (2012) RV Poseidon Cruise Report 436 [POS436]: North Kolbeinsey Ridge - geochemistry and volcanology, 06.07.2012 (Kiel) - 31.07.2012 (Akureyri). GEOMAR, Kiel, Germany, doi: 10.3289/CR_POS_436.
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All submarine samples were retrieved during recent research cruises in combination with new multibeam bathymetry (Pedersen et al., 2010; Devey, 2012).
View in article


Dick, H.J.B., Lin, J., Schouten, H. (2003) An ultraslow-spreading class of ocean ridge. Nature 426, 405-412.
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At slow to ultraslow spreading rates along mid-ocean ridges, thicker lithosphere typically impedes magma generation and tectonic extension can play a more significant role in crustal production (Dick et al., 2003).
View in article
Jan Mayen and its immediate environs in the North Atlantic (Fig. 1) include an intraplate, volcanically-active island or hotspot (Jan Mayen Island), positioned at the northern terminus of a small, rifted microcontinent (Jan Mayen Ridge; Johnson and Heezen, 1967; Kodaira et al., 1997; Gaina et al., 2009) and adjacent to two second-order ultraslow-spreading (Dick et al., 2003) ridge segments, the Northern Kolbeinsey Ridge (NKR) and Southern Mohns Ridge (SMR), and the Jan Mayen Fracture Zone, a major fracture zone with ~200 km of transform offset.
View in article
The Mohns Ridge is an ultraslow-spreading ridge (17 mm yr-1 full-spreading rate; Mosar et al., 2002; Dick et al., 2003) north of Jan Mayen Island with relatively thin crust (~4 km; Klingelhofer et al., 2000; Okino et al., 2002; Ljones et al., 2004; Kandilarov et al., 2008) and mainly characterised by highly oblique spreading expressed as a series of en echelon rift basins (Géli et al., 2012).
View in article
Unlike the Mohns Ridge, the Kolbeinsey Ridge is overall characterised by orthogonal spreading at ultraslow rates (18 mm yr-1; Mosar et al., 2002; Dick et al., 2003) and relatively thick ocean crust (7-10 km; Kodaira et al., 1997).
View in article
We hence assert that the distinct morphology and tectonically-dominated accretionary style typical of ultraslow spreading ridges (Dick et al., 2003) is particularly sensitive to even modest increases in mantle temperature and magma supply, which cause the ridge to take on growth properties more typical of slow- or intermediate-spreading ridges.
View in article


Elkins, L.J., Sims, K.W.W., Prytulak, J., Mattielli, N., Elliott, T., Blichert-Toft, J., Blusztajn, J., Dunbar, N., Devey, C. W., Mertz, D.F., Schilling, J.G. (2011) Understanding melt generation beneath the slow spreading Kolbeinsey Ridge from 238U, 230Th, and 231Pa excesses. Geochimica et Cosmochimica Acta 75, 6300-6329.
Show in context

Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
View in article
Figure 2 [...] The Kolbeinsey endmember, based on depleted values from a suite of published MKR measurements (Schilling et al., 1983; Blichert-Toft et al., 2005; Elkins et al., 2011) and NKR sample POS436 246DR-2, has εHf = +19.2, εNd = +10, 206Pb/204Pb = 18.0, 207Pb/204Pb = 15.43, and Hf, Nd, and Pb concentrations of 0.5, 3, and 0.3 ppm, respectively; mixtures of Jan Mayen and Kolbeinsey endmembers cannot fully explain NKR lava compositions.
View in article
Likewise, NKR αSm-Nd values (where αSm-Nd = (Sm/Nd)sample / (Sm/Nd)source, and (Sm/Nd)source is calculated from 143Nd/144Ndsample using a mantle model age of 1.8 Ga; DePaolo, 1988; Sims et al., 1995; Salters, 1996) are more typical of global MORB (<1.0), unlike other Kolbeinsey Ridge basalts with αSm-Nd > 1.0 (Salters, 1996; Elkins et al., 2011), supporting a distinct mantle source beneath the NKR.
View in article
While high (230Th/238U) activity ratios have suggested melting of a depleted garnet peridotite source for the MKR, NKR lavas have low (231Pa/235U) activity ratios, likely the product of rapid melting of garnet-bearing eclogite (Elkins et al., 2011, 2014).
View in article
Figure 3 [...] The variation between Jan Mayen Island/SMR and the NKR likely reflects a heterogeneous mantle source. (b) αSm-Nd; because Sm is always more compatible than Nd during melting, values less than unity reflect the degree of melting of the model source, while values greater than unity (e.g., MKR basalts; Salters, 1996; Elkins et al., 2011) require a different source composition and/or younger age than recorded by radiogenic isotopes.
View in article
For example, the more enriched basalts collected from the Eggvin Bank exhibit lower (Sm/Yb)N ratios than the Jan Mayen endmember (Table S-2, Figs. 3, S-1), which cannot be explained by a lack of residual garnet in the source, since NKR magmas are known to be products of melting in the presence of garnet from 230Th/238U > 1 (Elkins et al., 2011, 2014).
View in article


Elkins, L.J., Sims, K.W.W., Prytulak, J., Blichert-Toft, J., Elliott, T., Blusztajn, J., Fretzdorff, S., Reagan, M., Haase, K., Humphris, S., Schilling, J.G. (2014) Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges. Geochimica et Cosmochimica Acta 127, 140-170.
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Typical Mohns Ridge MORB are characterised by relatively high incompatible element contents and enriched radiogenic isotope values (Schilling et al., 1999; 2005; Elkins et al., 2014), but with relatively high 208Pb/204Pb and 207Pb/204Pb for a given 206Pb/204Pb, akin to the so-called DUPAL anomaly observed in the southern oceans (Blichert-Toft et al., 2005).
View in article
Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
View in article
Figure 2 [...] The hypothesised Mohns endmember, extrapolated to values that best explain available SMR samples as binary mixtures of Jan Mayen-Mohns Ridge lavas, has εHf = +24, εNd = +10.1, 206Pb/204Pb = 17.9, 207Pb/204Pb = 15.41, and Hf, Nd, and Pb concentrations of 5.6, 30, and 0.7, ppm, respectively; this composition is reasonable compared to published measurements from the Mohns Ridge (Schilling et al., 1983; Schilling et al., 1999; Blichert-Toft et al., 2005; Elkins et al., 2014).
View in article
Kolbeinsey Ridge basalts overall have notable depletions in incompatible trace elements and long-lived radiogenic isotope signatures, with high (230Th/238U) activity ratios, together suggesting high degrees of melting of a depleted garnet peridotite source (Elkins et al., 2014).
View in article
While high (230Th/238U) activity ratios have suggested melting of a depleted garnet peridotite source for the MKR, NKR lavas have low (231Pa/235U) activity ratios, likely the product of rapid melting of garnet-bearing eclogite (Elkins et al., 2011, 2014).
View in article
For example, the more enriched basalts collected from the Eggvin Bank exhibit lower (Sm/Yb)N ratios than the Jan Mayen endmember (Table S-2, Figs. 3, S-1), which cannot be explained by a lack of residual garnet in the source, since NKR magmas are known to be products of melting in the presence of garnet from 230Th/238U > 1 (Elkins et al., 2011, 2014).
View in article
In addition to the 231Pa/235U evidence for eclogite (Elkins et al., 2014), partition coefficients for Pb, Si, Al, and Fe in eclogite support an eclogite-rich source contributing magmas with the relatively high Pb and SiO2 and low FeO and Al2O3 observed in NKR MORB (Haase et al., 2003; Pertermann and Hirschmann, 2003) (Tables S-2, S-3, Figs. S-2, S-3, S-4).
View in article


Gaina, C., Gernigon, L., Ball, P. (2009) Palaeocene-Recent plate boundaries in the NE Atlantic and the formation of the Jan Mayen microcontinent. Journal of the Geological Society of London 166, 601-616.
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Jan Mayen and its immediate environs in the North Atlantic (Fig. 1) include an intraplate, volcanically-active island or hotspot (Jan Mayen Island), positioned at the northern terminus of a small, rifted microcontinent (Jan Mayen Ridge; Johnson and Heezen, 1967; Kodaira et al., 1997; Gaina et al., 2009) and adjacent to two second-order ultraslow-spreading (Dick et al., 2003) ridge segments, the Northern Kolbeinsey Ridge (NKR) and Southern Mohns Ridge (SMR), and the Jan Mayen Fracture Zone, a major fracture zone with ~200 km of transform offset.
View in article


Gale, A., Dalton, C.A., Langmuir, C.H., Su, Y., Schilling, J.G. (2013) The mean composition of ocean ridge basalts. Geochemistry Geophysics Geosystems 14, 489-518.
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The normal accretion process along divergent plate boundaries can be notably altered in hotspot-ridge interaction settings, where elevated mantle temperature anomalies enhance mantle melting, generating unusually thick oceanic crust (e.g., Schilling et al., 1985; Schilling, 1991; Gale et al., 2013; Gale et al., 2014).
View in article


Gale, A., Langmuir, C.H., Dalton, C.A. (2014) The global systematics of ocean ridge basalts and their origin. Journal of Petrology 55, 1051-1082.
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The normal accretion process along divergent plate boundaries can be notably altered in hotspot-ridge interaction settings, where elevated mantle temperature anomalies enhance mantle melting, generating unusually thick oceanic crust (e.g., Schilling et al., 1985; Schilling, 1991; Gale et al., 2013; Gale et al., 2014).
View in article


Géli, L., Renard, V., Rommevaux, C. (2012) Ocean crust formation processes at very slow spreading centers: A model for the Mohns RIdge, near 72ºN, based on magnetic, gravity, and seismic data. Journal of Geophysical Research: Solid Earth 99, 2995-3013.
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The Mohns Ridge is an ultraslow-spreading ridge (17 mm yr-1 full-spreading rate; Mosar et al., 2002; Dick et al., 2003) north of Jan Mayen Island with relatively thin crust (~4 km; Klingelhofer et al., 2000; Okino et al., 2002; Ljones et al., 2004; Kandilarov et al., 2008) and mainly characterised by highly oblique spreading expressed as a series of en echelon rift basins (Géli et al., 2012).
View in article


Haase, K.M., Devey, C.W., Mertz, D.F., Stoffers, P., Garbe-Schönberg, D. (1996) Geochemistry of lavas from Mohns ridge, Norwegian-Greenland Sea: Implications for melting conditions and magma sources near Jan Mayen. Contributions to Mineralogy and Petrology 123, 223-237.
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The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984; Mertz et al., 1991; Haase et al., 1996; Schilling et al., 1999; Trønnes et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005; Debaille et al., 2009).
View in article
The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen’s high magma production rate and enriched chemistry (Imsland, 1986; Maaløe et al., 1986; Thy et al., 1991): cold edge effects near the fracture zone (Mertz et al., 1991; Haase et al., 1996), variably melting source heterogeneities (Mertz et al., 1991; Haase et al., 2003; Mertz et al., 2004), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005), or a locally wet mantle (Haase et al., 2003; Mertz et al., 2004).
View in article
The abrupt change in purported mantle composition across the Jan Mayen Fracture Zone has been interpreted to indicate a sharp chemical discontinuity, perhaps reflecting a major mantle flow boundary (Haase et al., 1996) (Fig. 3).
View in article


Haase, K.M., Devey, C.W., Wieneke, M. (2003) Magmatic processes and mantle heterogeneity beneath the slow-spreading northern Kolbeinsey Ridge segment, North Atlantic. Contributions to Mineralogy and Petrology 144, 428-448.
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The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984; Mertz et al., 1991; Haase et al., 1996; Schilling et al., 1999; Trønnes et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005; Debaille et al., 2009).
View in article
The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen’s high magma production rate and enriched chemistry (Imsland, 1986; Maaløe et al., 1986; Thy et al., 1991): cold edge effects near the fracture zone (Mertz et al., 1991; Haase et al., 1996), variably melting source heterogeneities (Mertz et al., 1991; Haase et al., 2003; Mertz et al., 2004), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005), or a locally wet mantle (Haase et al., 2003; Mertz et al., 2004).
View in article
Former work identified more enriched isotopic and trace element signatures on the Eggvin Bank and NKR than the MKR, generally attributed to the influence of the Jan Mayen hotspot (Schilling et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005).
View in article
In addition to the 231Pa/235U evidence for eclogite (Elkins et al., 2014), partition coefficients for Pb, Si, Al, and Fe in eclogite support an eclogite-rich source contributing magmas with the relatively high Pb and SiO2 and low FeO and Al2O3 observed in NKR MORB (Haase et al., 2003; Pertermann and Hirschmann, 2003) (Tables S-2, S-3, Figs. S-2, S-3, S-4).
View in article


Hanan, B.B., Blichert-Toft, J., Kingsley, R., Schilling, J.G. (2000) Depleted Iceland mantle plume geochemical signature: artifact of multicomponent mixing? Geochemistry Geophysics Geosystems 1, doi: 10.1029/1999GC000009.
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While similar, Jan Mayen area lavas exhibit a distinct geochemical composition from Icelandic lavas (e.g., higher 87Sr/86Sr and Pb isotope ratios, lower 143Nd/144Nd and 176Hf/177Hf, normal MORB 3He/4He, and distinct 187Os/188Os on Jan Mayen Island; Schilling et al., 1999; Hanan et al., 2000; Blichert-Toft et al., 2005; Debaille et al., 2009), suggesting an enriched source discrete from the Icelandic hotspot source, possibly entraining subcontinental lithospheric mantle (SCLM) (Debaille et al., 2009).
View in article


Hemond, C., Arndt, N.T., Lichtenstein, U., Hofmann, A.W., Oskarsson, N., Steinthorsson, S. (1993) The Heterogeneous Iceland Plume - Nd-Sr-O Isotopes and Trace-Element Constraints. Journal of Geophysical Research-Solid Earth 98, 15833-15850.
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
View in article


Imsland, P. (1986) The volcanic eruption on Jan Mayen, January 1985: Interaction between a volcanic island and a fracture zone. Journal of Volcanology and Geothermal Research 28, 45-53.
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The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen’s high magma production rate and enriched chemistry (Imsland, 1986; Maaløe et al., 1986; Thy et al., 1991): cold edge effects near the fracture zone (Mertz et al., 1991; Haase et al., 1996), variably melting source heterogeneities (Mertz et al., 1991; Haase et al., 2003; Mertz et al., 2004), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005), or a locally wet mantle (Haase et al., 2003; Mertz et al., 2004).
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Johnson, G.L., Heezen, B.C. (1967) Arctic Mid-Oceanic Ridge. Nature 215, 724-728.
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Jan Mayen and its immediate environs in the North Atlantic (Fig. 1) include an intraplate, volcanically-active island or hotspot (Jan Mayen Island), positioned at the northern terminus of a small, rifted microcontinent (Jan Mayen Ridge; Johnson and Heezen, 1967; Kodaira et al., 1997; Gaina et al., 2009) and adjacent to two second-order ultraslow-spreading (Dick et al., 2003) ridge segments, the Northern Kolbeinsey Ridge (NKR) and Southern Mohns Ridge (SMR), and the Jan Mayen Fracture Zone, a major fracture zone with ~200 km of transform offset.
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Kandilarov, A., Mjelde, R., Okino, K., Murai, Y. (2008) Crustal structure of the ultra-slow spreading Knipovich Ridge, North Atlantic, along a presumed amagmatic portion of oceanic crustal formation. Marine Geophysical Researches 29, 109-134.
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The Mohns Ridge is an ultraslow-spreading ridge (17 mm yr-1 full-spreading rate; Mosar et al., 2002; Dick et al., 2003) north of Jan Mayen Island with relatively thin crust (~4 km; Klingelhofer et al., 2000; Okino et al., 2002; Ljones et al., 2004; Kandilarov et al., 2008) and mainly characterised by highly oblique spreading expressed as a series of en echelon rift basins (Géli et al., 2012).
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Kandilarov, A., Mjelde, R., Pedersen, R.B., Hellevang, B., Papenberg, C., Petersen, C.J., Planert, L., Flueh, E. (2012) The northern boundary of the Jan Mayen microcontinent, North Atlantic determined from ocean bottom seismic, multichannel seismic, and gravity data. Marine Geophysical Research 33, 55-76.
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In contrast, its southern segment (the SMR) has an orthogonal spreading direction and irregular off-axis crustal morphology, with a shallower ridge axis and thicker crust (~10 km; Kandilarov et al., 2012) (Fig. 1).
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Kempton, P.D., Fitton, J.G., Saunders, A.D., Nowell, G.M., Taylor, R.N., Hardarson, B.S., Pearson, G. (2000) The Iceland plume in space and time: a Sr-Nd-Pb-Hf study of the North Atlantic rifted margin. Earth and Planetary Science Letters 177, 255-271.
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
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Klingelhofer, F., Géli, L., White, R.S. (2000) Geophysical and geochemical constraints on crustal accretion at the very-slow spreading Mohns Ridge. Geophysical Research Letters 27, 1547-1550.
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The Mohns Ridge is an ultraslow-spreading ridge (17 mm yr-1 full-spreading rate; Mosar et al., 2002; Dick et al., 2003) north of Jan Mayen Island with relatively thin crust (~4 km; Klingelhofer et al., 2000; Okino et al., 2002; Ljones et al., 2004; Kandilarov et al., 2008) and mainly characterised by highly oblique spreading expressed as a series of en echelon rift basins (Géli et al., 2012).
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Kodaira, S., Mjelde, R., Gunnarsson, K., Shiobara, H., Shimamura, H. (1997) Crustal structure of the Kolbeinsey Ridge, North Atlantic, obtained by use of ocean bottom seismographs. Journal of Geophysical Research-Solid Earth 102, 3131-3151.
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Jan Mayen and its immediate environs in the North Atlantic (Fig. 1) include an intraplate, volcanically-active island or hotspot (Jan Mayen Island), positioned at the northern terminus of a small, rifted microcontinent (Jan Mayen Ridge; Johnson and Heezen, 1967; Kodaira et al., 1997; Gaina et al., 2009) and adjacent to two second-order ultraslow-spreading (Dick et al., 2003) ridge segments, the Northern Kolbeinsey Ridge (NKR) and Southern Mohns Ridge (SMR), and the Jan Mayen Fracture Zone, a major fracture zone with ~200 km of transform offset.
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Unlike the Mohns Ridge, the Kolbeinsey Ridge is overall characterised by orthogonal spreading at ultraslow rates (18 mm yr-1; Mosar et al., 2002; Dick et al., 2003) and relatively thick ocean crust (7-10 km; Kodaira et al., 1997).
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Ljones, F., Kuwano, A., Mjelde, R., Breivik, A., Shimamura, H., Murai, Y., Nishimura, Y. (2004) Crustal transect from the North Atlantic Knipovich Ridge to the Svalbard margin west of hornsund. Tectonophysics 378, 17-41.
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The Mohns Ridge is an ultraslow-spreading ridge (17 mm yr-1 full-spreading rate; Mosar et al., 2002; Dick et al., 2003) north of Jan Mayen Island with relatively thin crust (~4 km; Klingelhofer et al., 2000; Okino et al., 2002; Ljones et al., 2004; Kandilarov et al., 2008) and mainly characterised by highly oblique spreading expressed as a series of en echelon rift basins (Géli et al., 2012).
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Maaløe, S., Sørensen, I. B., Hertogen, J. (1986) The trachybasaltic suite of Jan Mayen. Journal of Petrology 27, 439-466.
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The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen’s high magma production rate and enriched chemistry (Imsland, 1986; Maaløe et al., 1986; Thy et al., 1991): cold edge effects near the fracture zone (Mertz et al., 1991; Haase et al., 1996), variably melting source heterogeneities (Mertz et al., 1991; Haase et al., 2003; Mertz et al., 2004), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005), or a locally wet mantle (Haase et al., 2003; Mertz et al., 2004).
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Three additional, subaerial alkali basalts from Jan Mayen Island are included for literature comparison (Maaløe et al., 1986).
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Table 1 [...] Subaerial samples (samples from Maaløe et al. [17]):
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Mahoney, J.J., Sinton, J.M., Kurz, M.D., Macdougall, J.D., Spencer, K.J., Lugmair, G.W. (1994) Isotope and trace element characteristics of a super-fast spreading ridge: East Pacific Rise, 13-23ºS. Earth and Planetary Science Letters 121, 173-193.
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For comparison, the 17 ºS location on the East Pacific Rise is adjacent to a small hotspot but shows little geomorphological impact at fast spreading rates (Mahoney et al., 1994).
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Mertz, D.F., Devey, C.W., Todt, W., Stoffers, P., Hofmann, A.W. (1991) Sr-Nd-Pb Isotope Evidence against Plume Asthenosphere Mixing North of Iceland. Earth and Planetary Science Letters 107, 243-255.
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The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984; Mertz et al., 1991; Haase et al., 1996; Schilling et al., 1999; Trønnes et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005; Debaille et al., 2009).
View in article
The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen’s high magma production rate and enriched chemistry (Imsland, 1986; Maaløe et al., 1986; Thy et al., 1991): cold edge effects near the fracture zone (Mertz et al., 1991; Haase et al., 1996), variably melting source heterogeneities (Mertz et al., 1991; Haase et al., 2003; Mertz et al., 2004), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005), or a locally wet mantle (Haase et al., 2003; Mertz et al., 2004).
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Mertz, D.F., Sharp, W.D., Haase, K.M. (2004) Volcanism on the Eggvin Bank (Central Norwegian-Greenland Sea, latitude similar to 71 degrees N): age, source, and relationship to the Iceland and putative Jan Mayen plumes. Journal of Geodynamics 38, 57-83.
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The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984; Mertz et al., 1991; Haase et al., 1996; Schilling et al., 1999; Trønnes et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005; Debaille et al., 2009).
View in article
The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen’s high magma production rate and enriched chemistry (Imsland, 1986; Maaløe et al., 1986; Thy et al., 1991): cold edge effects near the fracture zone (Mertz et al., 1991; Haase et al., 1996), variably melting source heterogeneities (Mertz et al., 1991; Haase et al., 2003; Mertz et al., 2004), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005), or a locally wet mantle (Haase et al., 2003; Mertz et al., 2004).
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Former work identified more enriched isotopic and trace element signatures on the Eggvin Bank and NKR than the MKR, generally attributed to the influence of the Jan Mayen hotspot (Schilling et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005).
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Mosar, J., Lewis, G., Torsvik, T.H. (2002) North Atlantic sea-floor spreading rates: implications for the Tertiary development of inversion structures of the Norwegian-Greenland Sea. Journal of the Geological Society of London 159, 503-515.
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The Mohns Ridge is an ultraslow-spreading ridge (17 mm yr-1 full-spreading rate; Mosar et al., 2002; Dick et al., 2003) north of Jan Mayen Island with relatively thin crust (~4 km; Klingelhofer et al., 2000; Okino et al., 2002; Ljones et al., 2004; Kandilarov et al., 2008) and mainly characterised by highly oblique spreading expressed as a series of en echelon rift basins (Géli et al., 2012).
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Unlike the Mohns Ridge, the Kolbeinsey Ridge is overall characterised by orthogonal spreading at ultraslow rates (18 mm yr-1; Mosar et al., 2002; Dick et al., 2003) and relatively thick ocean crust (7-10 km; Kodaira et al., 1997).
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While ultraslow ridges are typically characterised by thin crust, tectonic spreading, and peridotite exposure, those features are not observed in the Jan Mayen region despite ultraslow full-spreading rates of 17-18 mm yr-1 (Mosar et al., 2002).
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Neumann, E.R., Schilling, J.G. (1984) Petrology of Basalts from the Mohns-Knipovich Ridge - the Norwegian-Greenland Sea. Contributions to Mineralogy and Petrology 85, 209-223.
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The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984; Mertz et al., 1991; Haase et al., 1996; Schilling et al., 1999; Trønnes et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005; Debaille et al., 2009).
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Nowell, G.M., Kempton, P.D., Noble, S.R., Fitton, J.G., Saunders, A.D., Mahoney, J.J., Taylor, R.N. (1998) High precision Hf isotope measurements of MORB and OIB by thermal ionisation mass spectrometry; insights into the depleted mantle. Chemical Geology 149, 211-233.
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
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Okino, K., Curewitz, D., Asada, M., Tamaki, K., Vogt, P., Crane, K. (2002) Preliminary analysis of the Knipovich Ridge segmentation: influence of focused magmatism and ridge obliquity on an ultraslow spreading system. Earth and Planetary Science Letters 202, 275-288.
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The Mohns Ridge is an ultraslow-spreading ridge (17 mm yr-1 full-spreading rate; Mosar et al., 2002; Dick et al., 2003) north of Jan Mayen Island with relatively thin crust (~4 km; Klingelhofer et al., 2000; Okino et al., 2002; Ljones et al., 2004; Kandilarov et al., 2008) and mainly characterised by highly oblique spreading expressed as a series of en echelon rift basins (Géli et al., 2012).
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Óskarsson, N., Sigvaldason, G., Steinthorsson, S. (1982) A dynamic model of rift zone petrogenesis and the regional petrology of Iceland. Journal of Petrology 23, 28-74.
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
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Pedersen, R.B., Thorseth, I.H., Nygård, T.E., Lilley, M.D., Kelley, D.S. (2010) Hydrothermal activity at the Arctic mid-ocean ridges. In: Rona, P.A., Devey, C.W., Dyment, J., Murton, B.J. (Eds.) Diversity of Hydrothermal Systems on Slow Spreading Ocean Ridges. AGU, 67-89.
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All submarine samples were retrieved during recent research cruises in combination with new multibeam bathymetry (Pedersen et al., 2010; Devey, 2012).
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Recent mapping indicates the presence of large, partly eroded volcanic structures, often bisected by faulting (Pedersen et al., 2010).
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Pertermann, M., Hirschmann, M. (2003) Partial melting experiments on MORB-like pyroxenite between 2 and 3 GPa: Constraints on the presence of pyroxenite in basalt source regions from solidus location and melting rate. Journal of Geophysical Research 108, doi: 10.1029/2000JB000118.
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In addition to the 231Pa/235U evidence for eclogite (Elkins et al., 2014), partition coefficients for Pb, Si, Al, and Fe in eclogite support an eclogite-rich source contributing magmas with the relatively high Pb and SiO2 and low FeO and Al2O3 observed in NKR MORB (Haase et al., 2003; Pertermann and Hirschmann, 2003) (Tables S-2, S-3, Figs. S-2, S-3, S-4).
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Salters, V.J.M. (1996) The generation of mid-ocean ridge basalts from the Hf and Nd isotope perspective. Earth and Planetary Science Letters 141, 109-123.
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Likewise, NKR αSm-Nd values (where αSm-Nd = (Sm/Nd)sample / (Sm/Nd)source, and (Sm/Nd)source is calculated from 143Nd/144Ndsample using a mantle model age of 1.8 Ga; DePaolo, 1988; Sims et al., 1995; Salters, 1996) are more typical of global MORB (<1.0), unlike other Kolbeinsey Ridge basalts with αSm-Nd > 1.0 (Salters, 1996; Elkins et al., 2011), supporting a distinct mantle source beneath the NKR.
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Figure 3 [...] The variation between Jan Mayen Island/SMR and the NKR likely reflects a heterogeneous mantle source. (b) αSm-Nd; because Sm is always more compatible than Nd during melting, values less than unity reflect the degree of melting of the model source, while values greater than unity (e.g., MKR basalts; Salters, 1996; Elkins et al., 2011) require a different source composition and/or younger age than recorded by radiogenic isotopes.
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Salters, V.J.M., White, W.M. (1998) Hf isotope constraints on mantle evolution. Chemical Geology 145, 447-460.
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
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Schilling, J.G. (1991) Fluxes and excess temperatures of mantle plumes inferred from their interaction with migrating mid-ocean ridges. Nature 352, 397-403.
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The normal accretion process along divergent plate boundaries can be notably altered in hotspot-ridge interaction settings, where elevated mantle temperature anomalies enhance mantle melting, generating unusually thick oceanic crust (e.g., Schilling et al., 1985; Schilling, 1991; Gale et al., 2013; Gale et al., 2014).
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Schilling, J.G., Zajac, M., Evans, R., Johnston, T., White, W., Devine, J.D., Kingsley, R. (1983) Petrologic and Geochemical Variations Along the Mid-Atlantic Ridge from 29-Degrees-N to 73-Degrees-N. American Journal of Science 283, 510-586.
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Figure 2 [...] The hypothesised Mohns endmember, extrapolated to values that best explain available SMR samples as binary mixtures of Jan Mayen-Mohns Ridge lavas, has εHf = +24, εNd = +10.1, 206Pb/204Pb = 17.9, 207Pb/204Pb = 15.41, and Hf, Nd, and Pb concentrations of 5.6, 30, and 0.7, ppm, respectively; this composition is reasonable compared to published measurements from the Mohns Ridge (Schilling et al., 1983; Schilling et al., 1999; Blichert-Toft et al., 2005; Elkins et al., 2014).
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Figure 2 [...] The Kolbeinsey endmember, based on depleted values from a suite of published MKR measurements (Schilling et al., 1983; Blichert-Toft et al., 2005; Elkins et al., 2011) and NKR sample POS436 246DR-2, has εHf = +19.2, εNd = +10, 206Pb/204Pb = 18.0, 207Pb/204Pb = 15.43, and Hf, Nd, and Pb concentrations of 0.5, 3, and 0.3 ppm, respectively; mixtures of Jan Mayen and Kolbeinsey endmembers cannot fully explain NKR lava compositions.
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Schilling, J.G., Thompson, G., Kingsley, R., Humphris, S. (1985) Hotspot-migrating ridge interaction in the South Atlantic. Nature 313, 187-191.
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The normal accretion process along divergent plate boundaries can be notably altered in hotspot-ridge interaction settings, where elevated mantle temperature anomalies enhance mantle melting, generating unusually thick oceanic crust (e.g., Schilling et al., 1985; Schilling, 1991; Gale et al., 2013; Gale et al., 2014).
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Schilling, J.G., Kingsley, R., Fontignie, D., Poreda, R., Xue, S. (1999) Dispersion of the Jan Mayen and Iceland mantle plumes in the Arctic: A He-Pb-Nd-Sr isotope tracer study of basalts from the Kolbeinsey, Mohns, and Knipovich Ridges. Journal of Geophysical Research-Solid Earth 104, 10543-10569.
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The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984; Mertz et al., 1991; Haase et al., 1996; Schilling et al., 1999; Trønnes et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005; Debaille et al., 2009).
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Although different in key ways, broad geochemical similarities between Jan Mayen Island and Icelandic lavas have suggested the influence of a mantle plume (either a unique Jan Mayen plume or emplaced Icelandic material) on mantle melting beneath Jan Mayen Island (Schilling et al., 1999; Trønnes et al., 1999; Debaille et al., 2009).
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While similar, Jan Mayen area lavas exhibit a distinct geochemical composition from Icelandic lavas (e.g., higher 87Sr/86Sr and Pb isotope ratios, lower 143Nd/144Nd and 176Hf/177Hf, normal MORB 3He/4He, and distinct 187Os/188Os on Jan Mayen Island; Schilling et al., 1999; Hanan et al., 2000; Blichert-Toft et al., 2005; Debaille et al., 2009), suggesting an enriched source discrete from the Icelandic hotspot source, possibly entraining subcontinental lithospheric mantle (SCLM) (Debaille et al., 2009).
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Typical Mohns Ridge MORB are characterised by relatively high incompatible element contents and enriched radiogenic isotope values (Schilling et al., 1999; 2005; Elkins et al., 2014), but with relatively high 208Pb/204Pb and 207Pb/204Pb for a given 206Pb/204Pb, akin to the so-called DUPAL anomaly observed in the southern oceans (Blichert-Toft et al., 2005).
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
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Figure 2 [...] The hypothesised Mohns endmember, extrapolated to values that best explain available SMR samples as binary mixtures of Jan Mayen-Mohns Ridge lavas, has εHf = +24, εNd = +10.1, 206Pb/204Pb = 17.9, 207Pb/204Pb = 15.41, and Hf, Nd, and Pb concentrations of 5.6, 30, and 0.7, ppm, respectively; this composition is reasonable compared to published measurements from the Mohns Ridge (Schilling et al., 1983; Schilling et al., 1999; Blichert-Toft et al., 2005; Elkins et al., 2014).
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Former work identified more enriched isotopic and trace element signatures on the Eggvin Bank and NKR than the MKR, generally attributed to the influence of the Jan Mayen hotspot (Schilling et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005).
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Sims, K.W.W., Depaolo, D.J., Murrell, M.T., Baldridge, W.S., Goldstein, S.J., Clague, D.A. (1995) Mechanisms of Magma Generation beneath Hawaii and Midocean Ridges - Uranium/Thorium and Samarium/Neodymium Isotopic Evidence. Science 267, 508-512.
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Likewise, NKR αSm-Nd values (where αSm-Nd = (Sm/Nd)sample / (Sm/Nd)source, and (Sm/Nd)source is calculated from 143Nd/144Ndsample using a mantle model age of 1.8 Ga; DePaolo, 1988; Sims et al., 1995; Salters, 1996) are more typical of global MORB (<1.0), unlike other Kolbeinsey Ridge basalts with αSm-Nd > 1.0 (Salters, 1996; Elkins et al., 2011), supporting a distinct mantle source beneath the NKR.
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Sims, K.W.W., Maclennan, J., Blichert-Toft, J., Mervine, E. M., Blusztajn, J., Grönvold, K. (2013) Short length scale mantle heterogeneity beneath Iceland probed by glacial modulation of melting. Earth and Planetary Science Letters 379, 146-157.
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
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Smith, W.H.F., Sandwell, D.T. (1997) Global sea floor topography from satellite altimetry and ship depth soundings. Science 277, 1956-1962.
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Regional bathymetry (Smith and Sandwell, 1997) demonstrates the presence off-axis of shallow seafloor and highly segmented slopes persisting up to 30 km (~3 Ma) off-axis, further supporting a long-lived source of active volcanism.
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Stracke, A., Zindler, A., Salters, V.J.M., McKenzie, D., Blichert-Toft, J., Albarède, F., Gronvold, K. (2003) Theistareykir revisited. Geochemistry Geophysics Geosystems 4, doi: 10.1029/2001gc000201.
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
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Sun, S.S., Jahn, B. (1975) Lead and Strontium Isotopes in Postglacial Basalts from Iceland. Nature 255, 527-530.
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
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Thy, P., Lofgren, G.E., Imsland, P. (1991) Melting relations and the evolution of the Jan Mayen magma system. Journal of Petrology 32, 303-332.
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The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen’s high magma production rate and enriched chemistry (Imsland, 1986; Maaløe et al., 1986; Thy et al., 1991): cold edge effects near the fracture zone (Mertz et al., 1991; Haase et al., 1996), variably melting source heterogeneities (Mertz et al., 1991; Haase et al., 2003; Mertz et al., 2004), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005), or a locally wet mantle (Haase et al., 2003; Mertz et al., 2004).
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Trønnes, R.G., Planke, S., Sundvoll, B., Imsland, P. (1999) Recent volcanic rocks from Jan Mayen: Low-degree melt fractions of enriched northeast Atlantic mantle. Journal of Geophysical Research-Solid Earth 104, 7153-7168.
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The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984; Mertz et al., 1991; Haase et al., 1996; Schilling et al., 1999; Trønnes et al., 1999; Haase et al., 2003; Mertz et al., 2004; Blichert-Toft et al., 2005; Debaille et al., 2009).
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Although different in key ways, broad geochemical similarities between Jan Mayen Island and Icelandic lavas have suggested the influence of a mantle plume (either a unique Jan Mayen plume or emplaced Icelandic material) on mantle melting beneath Jan Mayen Island (Schilling et al., 1999; Trønnes et al., 1999; Debaille et al., 2009).
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In agreement with previous work (Trønnes et al., 1999; Debaille et al., 2009), Jan Mayen Island lavas are “enriched” with relatively high 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb and low eHf and eNd (e.g., 87Sr/86Sr = 0.703368-0.703490) (Table 1), and with trace element abundances resembling other ocean island basalts (Table S-2, Fig. S-1).
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The submarine samples from Jan Mayen Island appear relatively evolved compared to the most magnesian subaerial samples of this study (MgO = 5.1-6.45 vs. 10.6-11.1 wt. %; Table S-3), but as previously observed, there are no systematic trace element or isotopic variations correlating with differentiation, arguing against detectable crustal assimilation (Trønnes et al., 1999) (Tables 1, S-2, S-3).
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Zindler, A., Hart, S.R., Frey, F.A. (1979) Nd and Sr isotope ratios and rare earth element abundances in Reykjanes Peninsula basalts evidence for mantle heterogeneity beneath Iceland. Earth and Planetary Science Letters 45, 249-262.
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Figure 2 εNd vs. εHf, (b) εNd vs. 206Pb/204Pb, (c) 207Pb/204Pb vs. εHf, and (d) 207Pb/204Pb vs. 206Pb/204Pb diagrams for lavas from the Jan Mayen region and Iceland (Sun and Jahn, 1975; Zindler et al., 1979; Óskarsson et al., 1982; Hemond et al., 1993; Nowell et al., 1998; Salters and White, 1998; Schilling et al., 1999; Chauvel and Hémond, 2000; Kempton et al., 2000; Stracke et al., 2003; Blichert-Toft et al., 2005; Elkins et al., 2011; Sims et al., 2013; Elkins et al., 2014) (Tables 1, S-2).
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Supplementary Information


Methods

Submarine NKR, SMR, and Jan Mayen Island samples were retrieved by dredging or ROV sampling on the R/V Poseidon leg 436 (2012), R/V Håkon Mosby leg SM01 (2001), and R/V G.O. Sars leg CGB2011 (2011) (Fig. 1, Table 1), accompanying new high-resolution multibeam bathymetric mapping efforts for targeted sampling of fresh volcanic deposits. Samples were analysed for major and trace element concentrations and 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb compositions. Glassy submarine samples were handpicked for fresh volcanic glass to avoid visible alteration, palagonite, surface coatings, and phenocrysts. Two of the most primitive (high-MgO) subaerial samples from the Maaløe et al. (1986)

Maaløe, S., Sørensen, I.B., Hertogen, J. (1986) The trachybasaltic suite of Jan Mayen. Journal of Petrology 27, 439-466.

collection of Beerenberg Volcano on Jan Mayen Island and an additional more evolved (low-MgO) sample were selected for whole rock analysis to compare with submarine samples; major element concentrations of submarine Jan Mayen Island rocks with high crystalline contents were also measured by whole rock analysis. All whole rock material was prepared by hand crushing and grinding to small rock chips using an agate mortar and pestle.

Subaerial, crystalline rock samples JM-192, JM-71, and JM-84 were measured using whole rock analysis of rock chips, following removal of any altered rinds or large phenocrysts. Submarine samples SM01-DR-5-5 and SM01-DR-60-43 contained glassy, fresh groundmass from recent, historic lava flows, and were handpicked to remove any visible surface alteration or large phenocrysts. All other submarine samples were handpicked for pure, fresh, unaltered glass. To remove surface impurities, handpicked samples prepared for trace element and isotopic analysis at the University of Wyoming, the Ecole Normale Supérieure de Lyon, and Boston University were leached with 0.1 % oxalic acid + 2 % H2O2 for 15 minutes in an ultrasonic bath, followed by three rinses in ultrapure water, and then leached for an additional 15 minutes in an ultrasonic bath with 0.1 % HCl + 2 % H2O2 and again rinsed three times. Handpicked samples prepared at University of Bergen (Tables 1, S-2) were leached for 10 minutes in 1 % H2O2 in an ultrasonic bath, followed by three rinses in ultrapure water and then leached briefly in concentrated ultrapure HBr. Whole rock samples were ground to powder or small chips using an agate mortar and pestle for whole rock analysis.

Major elements for glassy samples were determined using an Electron Probe Microanalyzer JXA-8900 at the University of Maryland NanoCenter and the NispLab (Table S-3). For electron probe analysis of major elements, a minimum of 15 points were analysed per sample on one to four homogeneous, handpicked glass chips. For trace element analysis at Boston University, samples were dissolved using a HF-HNO3-HClO4 dissolution procedure and subsequently dried and redissolved in weak HNO3 for analysis by ICP-MS. At the University of Bergen, glass shards were analysed by LA-ICP-MS with a 120 mm diameter beam, pulse frequency of 10 Hz, beam energy of 0.3 mJ/pulse, and total ablation time of 90 s. NIST-glass CaO content (determined by electron microprobe) was used as a calibrating standard, and W-2 and BCR were analysed as unknowns in each sample batch, with accuracies of 2 to 8 % for rare earth elements.

Due to high crystallinity, subaerial samples from Jan Mayen Island were analysed for major elements by whole rock analysis of dissolved rock chips, and two fresh submarine samples dredged from the island’s flank were analysed in the same fashion using glassy groundmass hand-picked to remove large phenocrysts. All whole rock chips were then analysed for major elements at Boston University by ICP-AES (Table S-3) using methods after Murray et al. (2000)

Murray, R.W., Miller, D.J., Kryc, K. (2000) Analysis of major and trace elements in rocks, sedimens, and interstitial waters by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Ocean Drilling Program Technical Note 29, 1-27.

. Glass chips for NKR samples and a subsuite of SMR samples and the whole rock chips from Jan Mayen Island described above were further analysed for a full suite of trace element abundances at Boston University (Table S-2) (Murray et al., 2000

Murray, R.W., Miller, D.J., Kryc, K. (2000) Analysis of major and trace elements in rocks, sedimens, and interstitial waters by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Ocean Drilling Program Technical Note 29, 1-27.

; Scudder et al., 2014

Scudder, R.P., Murray, R.W., Schindlbeck, J.C., Kutterolf, S., Hauff, F., McKinley, C.C. (2014) Regional-scale input of dispersed and discrete volcanic ash to the Izu-Bonin and Mariana subduction zones. Geochemistry Geophysics Geosystems 15, 4369-4379.

; Dunlea et al., 2015

Dunlea, A.G., Murray, R.W., Sauvage, J., Spivack, A.J., Harris, R.N., D'Hondt, S. (2015) Dust, volcanic ash, and the evolution of the South Pacific Gyre through the Cenozoic. Palaeoceanography, doi: 10.1002/2015PA002829.

). Handpicked glass chips from the remaining SMR and Jan Mayen Island samples were analysed for major and trace elements in Bergen by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using a New Wave UP213 laser and a Finnigan Element2 ICP-MS at the University of Bergen (Tables S-2, S-3).

Northern Kolbeinsey Ridge basalt glass chips, a subsuite of SMR (Table S-1) basalt glass chips, and subaerial Jan Mayen Island basalt whole rock chips (see description above) were analysed for 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb compositions by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) (Nu Plasma 500 HR) at the Ecole Normale Supérieure de Lyon, all on the same sample dissolutions (Table 1). Splits from these same sample dissolutions were analysed for 87Sr/86Sr at the University of Wyoming, also by MC-ICP-MS (ThermoFinnigan™ NeptunePlus) (Table 1). Handpicked glass chips from additional SMR and Jan Mayen Island samples were analysed for 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb compositions at the University of Bergen (Table 1); 87Sr/86Sr was analysed by thermal ionisation mass spectrometry (TIMS) (Finnigan Mat262) and 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb compositions were measured by MC-ICP-MS (ThermoFinniganTM Neptune). Additional methods details provided in Supplementary Information.

206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 176Hf/177Hf, and 143Nd/144Nd isotope compositions measured by MC-ICP-MS in Lyon were analysed following the procedures in Blichert-Toft and Albarède (2009)

Blichert-Toft, J., Albarède, F. (2009) Mixing of isotopic heterogeneities in the Mauna Kea plume conduit. Earth and Planetary Science Letters 282, 190-200.

with the exception that Ln-Spec instead of HDEHP columns were used for Nd purification. Hafnium and Nd were normalised for instrumental mass bias relative to 179Hf/177Hf = 0.7325 and 146Nd/144Nd = 0.7219, respectively. 176Hf/177Hf of the JMC-475 Hf standard = 0.282160 ± 0.000010 (n = 45), and 143Nd/144Nd of the Rennes in-house standard = 0.511961 ± 0.000013 (n = 45) (Chauvel and Blichert-Toft, 2001

Chauvel, C., Blichert-Toft, J. (2001) A hafnium isotope and trace element perspective on melting of the depleted mantle. Earth and Planetary Science Letters 190, 137-151.

). Pb isotope compositions were analysed using Tl doping and sample-standard bracketing and the values of Eisele et al. (2003)

Eisele, J., Abouchami, W., Galer, S.J.G., Hofmann, A.W. (2003) The 320 kyr Pb isotope evolution of Mauna Kea lavas recorded in teh HSDP-2 drill core. Geochemistry Geophysics Geosystems 4, 8710.

for NIST 981. External reproducibilities of 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb are 100-200 ppm or 0.01-0.02 %. Hf, Nd, and Pb total procedural blanks were <20 pg.

Following partial separation in Lyon from the same sample dissolutions used for Hf, Nd, and Pb isotope work, Sr was purified at the University of Wyoming using cation-exchange resin in HCl followed by a Sr-Spec column to remove Rb. 87Sr/86Sr compositions were analysed using a ThermoFinnigan™ NeptunePlus MC-ICP-MS instrument with an Apex desolvating nebuliser. Strontium isotopes were analysed in static mode, using four Faraday collectors with ratios normalised to 86Sr/88Sr = 0.1194 to account for instrumental mass bias. Additional Faraday collectors were used to monitor Rb and Kr interferences, which were nearly undetectable at <0.0002 volts for 83Kr and ≤0.0001 volts for 85Rb in all analyses; any Kr interferences detected using the 83Kr peak were then corrected using natural abundances. Strontium isotope ratios are reported relative to NBS987 87Sr/86Sr = 0.71024. Total procedural blanks for Sr were <100 pg, and external reproducibility of 87Sr/86Sr for BCR-2 and other rock standards is ~ ±0.000016 (2σ).

At the University of Bergen Geoanalytical Facility, handpicked glass chips were dissolved in concentrated HF + HBr. Lead was extracted using methods after Manhes et al. (1978)

Manhes, G., Minster, J.F., Allègre, C.J. (1978) Comparative uranium-thorium-lead and rubidium-strontium study of Saint Sèverin amphoterite: consequences for early solar system chronology. Earth and Planetary Science Letters 39, 14-24.

and Sr, Nd, and Hf after Hamelin et al. (2013)

Hamelin, C., Bezos, A., Dosso, L., Escartin, J., Cannat, M., Mevel, C. (2013) Atypically depleted upper mantle component revealed by Hf isotopes at Lucky Strike segment. Chemical Geology 341, 128-139.

. 87Sr/86Sr was measured using a Finnigan Mat262 TIMS at the University of Bergen and 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb compositions were measured using a ThermoFinnigan Neptune MC-ICP-MS. Repeated measurements of international standard solutions during analyses yielded 87Sr/86Sr = 0.710238 ± 8 (n = 4, 2σ) for the NBS987 Sr standard, 143Nd/144Nd = 0.511845 ± 6 (n = 13, 2σ) for the LaJolla Nd standard, 177Hf/176Hf = 0.282148±3 (n = 15, 2σ) for the JMC-475 Hf standard, and 206Pb/204Pb = 16.9351 ± 13 (n = 8, 2σ), 207Pb/204Pb = 15.4889 ± 14 (n = 8, 2σ), and 208Pb/204Pb = 36.6879 ± 37 (n = 8, 2σ) for the NBS981 Pb standard. Instrumental mass fractionation of Pb was corrected for using the Tl doping and sample-standard bracketing technique. Data in Table 1 are reported relative to the following standard values: 87Sr/86Sr = 0.71024, 143Nd/144Nd = 0.511856, 177Hf/176Hf = 0.282157, 206Pb/204Pb = 16.9371, 207Pb/204Pb = 15.4913, and 208Pb/204Pb = 36.7213.

Supplementary Figures

Figure S-1 (a) Chondrite-normalised (McDonough and Sun, 1995

McDonough, W.F., Sun, S.S. (1995) The composition of the Earth. Chemical Geology 120, 223-253.

) REE concentrations and (b) N-MORB (Hofmann, 1988

Hofmann, A.W. (1988) Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust. Earth and Planetary Science Letters 90, 297-314.

) normalised trace element concentrations for samples from this study (Table S-2). NKR basalts have elevated Pb and HREE compared to Jan Mayen Island and the MKR, indicating that they cannot be simple mixtures of Kolbeinsey-type and Jan Mayen-type magmas. High (230Th/238U) ratios measured in NKR lavas also require the presence of garnet in the melt source, indicating that the trace element compositions in Eggvin Bank basalts is principally controlled by mantle source composition.
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Figure S-2 εHf vs. 206Pb/204Pb for the Jan Mayen region, with symbols, mixing trajectories, and references as in Figure 2.
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Figure S-3 (La/Sm) vs. FeO* for basalt samples from the Kolbeinsey Ridge and the NKR, using data from Haase et al. (2003)

Haase, K.M., Devey, C.W., Wieneke, M. (2003) Magmatic processes and mantle heterogeneity beneath the slow-spreading northern Kolbeinsey Ridge segment, North Atlantic. Contributions to Mineralogy and Petrology 144, 428-448.

and C. Devey, M. Wieneke, and K. Haase (unpub. data). Linear best-fit regression for Kolbeinsey Ridge samples suggests a slight positive relationship between FeO* and (La/Sm)N, likely controlled by degree of melting. Basalt rocks from the NKR are restricted to generally higher (La/Sm)N and lower FeO* values than the rest of the Kolbeinsey Ridge, best explained by an eclogite-bearing, incompatible element-enriched mantle source beneath the Eggvin Bank.
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Figure S-4 (a) 87Sr/86Sr vs. Pb, and (b) εNd vs. Pb. for the Jan Mayen region, with symbols and references as in Figure 2. The data support lithologically and isotopically heterogeneous mantle source compositions for the Jan Mayen region and corroborate the existence of an Eggvin Bank end-member distinct from Jan Mayen mantle.
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Supplementary Tables

Table S-1 Location information for new submarine samples analyzed in this study.
Sample number*LocationExpeditionbYearLatitude (ºN)Longitude (ºW)Depth (m)
StartStopStartStopStartStop
POS436 242DR-2bNKRR/V Poseidon Leg 436201270.7599770.7649813.5503513.5448315591436
POS436 246DR-2NKRR/V Poseidon Leg 436201270.7894270.7947213.7535013.7540017141630
POS436 235DR-1aNKRR/V Poseidon Leg 436201270.9127570.9123713.1240813.11248485381
POS436 253DR-E2NKRR/V Poseidon Leg 436201270.9489770.9474213.0347513.03770207175
POS436 253DR-6NKRR/V Poseidon Leg 436201270.9489770.9474213.0347513.03770207175
POS436 232DR-1NKRR/V Poseidon Leg 436201271.0598771.0565512.9523212.93983622578
POS436 209DR-2aNKRR/V Poseidon Leg 436201271.3134271.3159212.7027212.6944711991205
POS436 222DR-1NKRR/V Poseidon Leg 436201271.3470071.3472012.6433312.6292511391137
POS436 215DR-1NKRR/V Poseidon Leg 436201271.4766071.4759712.3938312.4061718191703
SM01-DR-24-14aJMR/V Håkon Mosby. SM012001-71.1287-7.8082-738
SM01-DR-23-3JMR/V Håkon Mosby. SM012001-71.1022-7.7913-697
SM01-DR-5-5JMR/V Håkon Mosby. SM012001-71.1192-7.9187-47
SM01-DR-60-43JMR/V Håkon Mosby. SM012001-71.1645-7.9880-222
SM01-DR-100-01SMRR/V Håkon Mosby. SM012001
70.9855-6.4003-2493
CGB-2011-D17-2aSMRR/V G.O. Sars. CGB2011201171.2616771.26135.843005.8397-847
SM01-DR70-1SMRR/V Håkon Mosby. SM012001-71.2382-6.1102-953
SM01-DR67-4SMRR/V Håkon Mosby. SM012001-71.2188-6.1713-806
SM01-DR-91-13SMRR/V Håkon Mosby. SM012001-71.2715-5.8468-732

* All samples collected by dredge, except ROV dive sample CGB-2011-D17-2a. For SM01 cruise, only end locations for dredges were recorded.
a SM01 and CGB-2011 sample depths are calculated from GEBCO global bathymetry (IOC, IHO, BODC, 2003 IOC, IHO, BODC (2003) Centenary Edition of the GEBCO Digital Atlas, published on CD-ROM on behalf of the Intergovernmental Oceanographic Commission and the International Hydrographic Organization as part of the General Bathymetric Chart of the Oceans, Liverpool, UK. ).
b R/V Poseidon sample information available in Earthchem/IEDA database (Elkins, 2015 Elkins, L.J. (2015) Jan Mayen glass and whole rock chemistry. IEDA/Earthchem data set, doi: 10.1594/IEDA/100536. ).

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Table S-2 Trace element abundance measured by ICP-MS.
SampleLocationLiScVCrCoNiCuZnRbSrZrYMoBaLa
Submarine samples:
POS436 242DR-2baNKR4.947.8274.7404.145.6127.188.079.27.5145.554.824.70.599.08.0
POS436 246DR-2aNKR4.546.9275.3246.049.485.7110.272.41.656.436.523.90.2-2.3
POS436 235DR-1aaNKR7.743.7424.418.143.820.149.9104.212.0150.0118.639.60.9172.215.4
POS436 253DR-E2aNKR6.836.9409.014.642.9174.649.1105.811.6140.4128.234.61.0175.715.1
POS436 253DR-6aNKR6.630.2402.319.443.238.873.8160.411.4138.1132.432.61.2173.213.7
POS436 232DR-1aNKR4.947.9280.4376.346.2106.392.373.84.299.246.825.50.452.75.2
POS436 209DR-2aaNKR6.752.9329.2173.947.655.777.489.96.4103.252.433.20.466.45.8
POS436 222DR-1aNKR5.547.4302.1226.047.074.388.483.24.8110.350.627.70.572.36.0
POS436 222DR-1 replicateaNKR5.449.2311.1233.248.574.491.687.35.2114.652.728.60.575.16.2
POS436 215DR-1aNKR5.838.3332.287.647.451.676.098.76.6100.161.825.60.6103.47.2
SM01-DR-24-14bJM---17.0-31.8--76.8764.4285.531.3-1192.471.6
SM01-DR-23-3bJM---3.7----90.5876.6404.639.6-1727.294.9
SM01-DR-5-5bJM---39.2-23.2--54.6556.9231.926.8-832.248.6
SM01-DR-60-43bJM---20.0-22.8--69.7674.7261.528.7-1051.656.5
SM01-DR-100-01bSMR---7.6-29.8--29.4315.9173.232.8-454.70.0
CGB-2011-D17-2aaSMR6.331.4367.823.441.828.354.8103.824.5326.2162.130.82.0453.728.8
SM01-DR70-1aSMR4.018.3361.524.442.233.563.995.320.9316.8165.119.32.1423.823.2
SM01-DR67-4aSMR7.025.4423.826.944.422.355.5107.639.7403.5227.630.4-639.145.0
SM01-DR-91-13bSMR---9.0-15.5--21.0244.6135.132.5-319.320.3
Subaerial samples (samples from Maaløe et al., 1986 Maaløe, S., Sørensen, I.B., Hertogen, J. (1986) The trachybasaltic suite of Jan Mayen. Journal of Petrology 27, 439-466. ):
JM-192aJM5.140.4284.7671.149.6167.534.087.133.0820.8279.230.51.8620.140.5
JM-71aJM4.835.3364.3533.051.9188.1100.081.441.6650.7287.525.32.3814.744.1
JM-84aJM7.727.1347.755.933.938.651.9102.8101.81156.9457.546.04.01546.790.8
Rock standard:
BHVO-2
4.429.1315.3327.648.4122.9132.2104.08.0365.8158.724.5-128.7929814.6
SampleCePrNdSmEuGdTbDyHoErYbLuHfPbUTh
Submarine samples:
POS436 242DR-2ba16.32.18.92.30.83.00.53.40.72.32.50.41.50.70.210.76
POS436 246DR-2a6.10.94.61.60.62.50.53.10.72.22.40.41.10.40.04-
POS436 235DR-1aa33.04.217.84.51.55.40.95.91.34.04.10.63.11.30.441.60
POS436 253DR-E2a34.44.117.44.31.45.00.95.41.13.63.70.63.41.40.491.54
POS436 253DR-6a32.43.715.33.71.24.40.84.71.03.23.30.53.31.70.481.49
POS436 232DR-1a11.01.57.02.10.82.90.53.50.82.42.60.41.40.60.130.37
POS436 209DR-2aa12.31.78.12.60.93.70.74.41.03.13.40.51.60.70.140.46
POS436 222DR-1a12.71.77.82.30.93.30.63.90.82.72.80.41.50.70.160.50
POS436 222DR-1 replicatea12.91.88.12.40.93.30.63.90.92.72.90.41.50.70.160.54
POS436 215DR-1a15.42.08.52.30.83.10.63.70.82.52.70.41.70.90.210.62
SM01-DR-24-14b144.216.260.110.23.17.81.06.11.13.02.60.46.5-2.318.56
SM01-DR-23-3b184.620.975.412.33.89.61.37.41.43.93.40.59.1-2.7510.39
SM01-DR-5-5b100.911.945.38.02.46.80.95.21.02.62.10.35.7-1.465.97
SM01-DR-60-43b123.214.052.79.02.87.31.05.51.02.72.30.36.2-1.917.34
SM01-DR-100-01b65.18.231.46.22.05.60.85.41.13.03.00.44.0-0.950.95
CGB-2011-D17-2aa60.97.127.75.71.85.60.95.01.03.03.00.54.01.70.933.44
SM01-DR70-1a58.05.621.33.91.23.40.52.90.61.71.60.24.01.90.992.46
SM01-DR67-4a85.510.739.87.62.26.71.05.91.13.22.90.45.32.44.861.29
SM01-DR-91-13b45.35.723.65.51.85.50.85.61.23.33.30.53.6-0.642.44
Subaerial samples (samples from Maaløe et al., 1986 Maaløe, S., Sørensen, I.B., Hertogen, J. (1986) The trachybasaltic suite of Jan Mayen. Journal of Petrology 27, 439-466. ):
JM-192a78.810.139.57.72.56.81.05.10.92.72.30.36.92.20.814.45
JM-71a80.110.137.96.92.15.70.84.20.82.22.00.36.92.51.145.08
JM-84a154.620.876.213.13.910.61.57.71.44.13.70.510.43.72.0612.22
Rock standard:
BHVO-236.15.423.86.02.05.90.95.20.92.41.90.34.31.61.230.41

a Trace elements measured by ICP-MS (VG Plasma Quad ExCell) at Boston University, with 1-2 % standard deviations.
b Trace elements measured by LA-ICP-MS (Thermo-Finnigan Element2) at the University of Bergen, with 2-5 % standard deviations.

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Table S-3 Major element composition results.
SampleLocationSiO2 Al2O3 TiO2 CaO MnOMgO FeOFe2O3 Na2O K2O Cr2O3 P2O5 Cl Total
Submarine samples:
POS436 242DR-2bNKR50.69(8)15.25(4)1.04(2)13.02(4)-8.37(5)8.66(5)-1.70(1)0.267(4)0.09(1)0.144(7)0.032(2)99.4(1)
POS436 246DR-2NKR50.73(9)15.02(4)0.85(3)13.64(6)-8.95(3)9.16(7)-1.57(1)0.074(3)0.07(1)0.094(7)0.012(1)100.3(1)
POS436 235DR-1aNKR52.27(9)13.06(4)2.25(5)8.68(5)-4.54(3)14.60(6)-2.76(2)0.551(4)0.031(9)0.22(1)0.141(3)99.3(2)
POS436 253DR-E2NKR52.5(2)11.9(9)2.0(1)9.8(6)-6.2(1.3)13.6(2)-2.5(3)0.45(5)0.03(1)0.20(2)0.14(2)99.5(2)
POS436 253DR-6NKR52.70(8)12.8(5)2.06(7)9.1(2)-5.4(7)13.66(7)-2.7(1)0.50(3)0.034(9)0.22(1)0.149(8)99.5(2)
POS436 232DR-1NKR50.90(7)14.83(3)1.00(3)13.16(5)-8.30(3)9.30(6)-1.777(9)0.192(2)0.07(1)0.074(5)0.028(1)99.8(1)
POS436 209DR-2aNKR52.2(1)13.03(4)2.28(3)8.68(3)-4.57(2)14.70(7)-2.75(2)0.568(2)0.05(1)0.233(8)0.143(2)99.4(2)
POS436 222DR-1NKR51.4(1)14.58(4)1.10(2)12.44(5)-7.56(7)10.22(5)-1.95(3)0.230(3)0.06(1)0.095(7)0.026(1)99.9(1)
POS436 215DR-1NKR52.24(7)14.24(4)1.25(3)11.09(6)-6.64(3)11.50(7)-2.088(8)0.309(3)0.027(7)0.121(8)0.038(2)99.7(1)
SM01-DR-24-14JM47.8(1)15.11(5)4.42(3)8.94(6)-3.70(2)12.20(6)-3.26(2)3.10(5)0.009(5)0.75(1)0.118(3)99.6(2)
SM01-DR-23-3JM56.8(1)17.14(4)2.14(4)4.56(4)-2.19(1)6.11(4)-3.7(2)3.93(2)0.020(6)0.453(8)0.191(3)97.5(2)
SM01-DR-5-5aJM48.0115.19075627563.2910.310.206.45-12.12.982.48-0.590.06101.7
SM01-DR-60-43aJM48.1716.13200506863.5110.410.205.05-12.83.022.67-0.620.12102.7
CGB-2011-D17-2aSMR51.4(2)14.57(7)2.44(2)9.77(6)-5.22(2)11.57(7)-2.90(1)1.003(8)0.015(7)0.367(9)0.152(2)99.6(3)
SM01-DR70-1SMR50.37(7)14.74(4)2.37(3)10.17(5)-5.62(2)10.5(1)-2.75(2)0.984(6)0.026(9)0.354(8)0.124(2)98.2(2)
SM01-DR67-4SMR51.18(9)14.35(8)2.86(3)9.08(4)-4.61(3)11.06(9)-2.85(4)1.40(3)0.029(9)0.476(9)0.109(3)98.2(2)
SM01-DR-91-13SMR52.1(2)14.17(4)2.34(3)9.8(2)-5.2(1)12.0(1)-2.5(2)0.75(1)0.025(7)0.298(8)0.069(2)99.4(2)
Subaerial samples (samples from Maaløe et al., 1986 Maaløe, S., Sørensen, I.B., Hertogen, J. (1986) The trachybasaltic suite of Jan Mayen. Journal of Petrology 27, 439-466. ):
JM-192aJM47.3912.922.5212.450.1711.13-11.12.201.13-0.43-101.4
JM-71aJM46.4112.842.4812.110.1710.61-11.02.161.15-0.42-99.3
JM-84aJM47.6516.523.269.880.195.02-11.13.592.05-0.68-100.0
Rock standard:
BHVO-2
48.8013.302.7411.200.167.17-12.12.110.50-0.27-98.4

* Major element concentrations of glass chips measured by EPMA methods unless otherwise indicated. EPMA results report uncertainties expressed in parentheses as 1s standard error for the last digit reported. Values shown are mean values of at least 15 analysed points, measured using a 20 keV beam. All Fe measured as FeO.
a Whole rock chips analysed for major element concentrations by ICP-ES (Jobin-Yovn Ultima-C) with standard deviations of 1-2 %. All Fe measured as Fe2O3.

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Supplementary Information References

Blichert-Toft, J., Albarède, F. (2009) Mixing of isotopic heterogeneities in the Mauna Kea plume conduit. Earth and Planetary Science Letters 282, 190-200.
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206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 176Hf/177Hf, and 143Nd/144Nd isotope compositions measured by MC-ICP-MS in Lyon were analysed following the procedures in Blichert-Toft and Albarède (2009) with the exception that Ln-Spec instead of HDEHP columns were used for Nd purification.
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Chauvel, C., Blichert-Toft, J. (2001) A hafnium isotope and trace element perspective on melting of the depleted mantle. Earth and Planetary Science Letters 190, 137-151.
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176Hf/177Hf of the JMC-475 Hf standard = 0.282160 ± 0.000010 (n = 45), and 143Nd/144Nd of the Rennes in-house standard = 0.511961 ± 0.000013 (n = 45) (Chauvel and Blichert-Toft, 2001).
View in Supplementary Information


Dunlea, A.G., Murray, R.W., Sauvage, J., Spivack, A.J., Harris, R.N., D'Hondt, S. (2015) Dust, volcanic ash, and the evolution of the South Pacific Gyre through the Cenozoic. Palaeoceanography, doi: 10.1002/2015PA002829.
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Glass chips for NKR samples and a subsuite of SMR samples and the whole rock chips from Jan Mayen Island described above were further analysed for a full suite of trace element abundances at Boston University (Table S-2) (Murray et al., 2000; Scudder et al., 2014; Dunlea et al., 2015).
View in Supplementary Information


Eisele, J., Abouchami, W., Galer, S.J.G., Hofmann, A.W. (2003) The 320 kyr Pb isotope evolution of Mauna Kea lavas recorded in teh HSDP-2 drill core. Geochemistry Geophysics Geosystems 4, 8710.
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Pb isotope compositions were analysed using Tl doping and sample-standard bracketing and the values of Eisele et al. (2003) for NIST 981.
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Elkins, L.J. (2015) Jan Mayen glass and whole rock chemistry. IEDA/Earthchem data set, doi: 10.1594/IEDA/100536.
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Table S-1
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Haase, K.M., Devey, C.W., Wieneke, M. (2003) Magmatic processes and mantle heterogeneity beneath the slow-spreading northern Kolbeinsey Ridge segment, North Atlantic. Contributions to Mineralogy and Petrology 144, 428-448.
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Figure S-3 (La/Sm)N­ vs. FeO* for basalt samples from the Kolbeinsey Ridge and the NKR, using data from Haase et al. (2003) and C. Devey, Martin Wieneke, and Karsten Haase (unpub. data).
View in article


Hamelin, C., Bezos, A., Dosso, L., Escartin, J., Cannat, M., Mevel, C. (2013) Atypically depleted upper mantle component revealed by Hf isotopes at Lucky Strike segment. Chemical Geology 341, 128-139.
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Lead was extracted using methods after Manhes et al. (1978) and Sr, Nd, and Hf after Hamelin et al. (2013).
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Hofmann, A.W. (1988) Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust. Earth and Planetary Science Letters 90, 297-314.
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Figure S-1 Chondrite-normalised (McDonough and Sun, 1995) REE concentrations and (b) N-MORB (Hofmann, 1988) normalised trace element concentrations for samples from this study (Table S-2).
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IOC, IHO, BODC (2003) Centenary Edition of the GEBCO Digital Atlas, published on CD-ROM on behalf of the Intergovernmental Oceanographic Commission and the International Hydrographic Organization as part of the General Bathymetric Chart of the Oceans, Liverpool, UK.
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Table S-1
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Maaløe, S., Sørensen, I.B., Hertogen, J. (1986) The trachybasaltic suite of Jan Mayen. Journal of Petrology 27, 439-466.
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Two of the most primitive (high-MgO) subaerial samples from the Maaløe et al. (1986) collection of Beerenberg Volcano on Jan Mayen Island and an additional more evolved (low-MgO) sample were selected for whole rock analysis to compare with submarine samples; major element concentrations of submarine Jan Mayen Island rocks with high crystalline contents were also measured by whole rock analysis.
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Table S-2
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Table S-3
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Manhes, G., Minster, J.F., Allègre, C.J. (1978) Comparative uranium-thorium-lead and rubidium-strontium study of Saint Sèverin amphoterite: consequences for early solar system chronology. Earth and Planetary Science Letters 39, 14-24.
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Lead was extracted using methods after Manhes et al. (1978) and Sr, Nd, and Hf after Hamelin et al. (2013).
View in Supplementary Information


McDonough, W.F., Sun, S.S. (1995) The composition of the Earth. Chemical Geology 120, 223-253.
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Figure S-1 Chondrite-normalised (McDonough and Sun, 1995) REE concentrations and (b) N-MORB (Hofmann, 1988) normalised trace element concentrations for samples from this study (Table S-2).
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Murray, R.W., Miller, D.J., Kryc, K. (2000) Analysis of major and trace elements in rocks, sedimens, and interstitial waters by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Ocean Drilling Program Technical Note 29, 1-27.
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All whole rock chips were then analysed for major elements at Boston University by ICP-AES (Table S-3) using methods after Murray et al. (2000).
View in Supplementary Information
Glass chips for NKR samples and a subsuite of SMR samples and the whole rock chips from Jan Mayen Island described above were further analysed for a full suite of trace element abundances at Boston University (Table S-2) (Murray et al., 2000; Scudder et al., 2014; Dunlea et al., 2015).
View in Supplementary Information


Scudder, R.P., Murray, R.W., Schindlbeck, J.C., Kutterolf, S., Hauff, F., McKinley, C.C. (2014) Regional-scale input of dispersed and discrete volcanic ash to the Izu-Bonin and Mariana subduction zones. Geochemistry Geophysics Geosystems 15, 4369-4379.
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Glass chips for NKR samples and a subsuite of SMR samples and the whole rock chips from Jan Mayen Island described above were further analysed for a full suite of trace element abundances at Boston University (Table S-2) (Murray et al., 2000; Scudder et al., 2014; Dunlea et al., 2015).
View in Supplementary Information

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