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Magma dynamics of ancient Mt. Etna inferred from clinopyroxene isotopic and trace element systematics

S.A. Miller1,

1Department of Earth Sciences, University of New Hampshire, 56 College Road, Durham, NH 03824, USA

M. Myers1,2,

1Department of Earth Sciences, University of New Hampshire, 56 College Road, Durham, NH 03824, USA
2Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, USA

M.F. Fahnestock1,

1Department of Earth Sciences, University of New Hampshire, 56 College Road, Durham, NH 03824, USA

J. Bryce1,

1Department of Earth Sciences, University of New Hampshire, 56 College Road, Durham, NH 03824, USA

J. Blichert-Toft3

3Laboratoire de Géologie de Lyon, Ecole Normale Supérieure de Lyon and Université Claude Bernard Lyon 1, CNRS UMR 5276, 46 Allée d’Italie, 69007 Lyon, France

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Miller, S.A., Myers, M., Fahnestock, M.F., Bryce, J.G., Blichert-Toft, J. (2017) Magma dynamics of ancient Mt. Etna inferred from clinopyroxene isotopic and trace element systematics. Geochem. Persp. Let. 4, 47-52.

NSF grant EAR-1057611 to JGB and SAM, the UNH Undergraduate Research Opportunities Program to MM, and the French Agence Nationale de la Recherche (grant ANR-10-BLANC-0603 M&Ms – Mantle Melting – Measurements, Models, Mechanisms) to JBT.

Geochemical Perspectives Letters v4  |  doi: 10.7185/geochemlet.1735
Received 16 March 2017  |  Accepted 3 August 2017  |  Published 28 September 2017
Copyright © 2017 European Association of Geochemistry

Keywords: Etna, hafnium, neodymium, lead, isotope, trace elements, peridotite, pyroxenite, mantle, assimilation, Timpe Santa Caterina, thermobarometry, clinopyroxene, basalt



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Abstract


Dynamic magmatic processes driving volcanic eruptions, including melting, fractionation, and assimilation, provide critical insights into plumbing systems supporting long-lived magmatism. Here we describe an approach combining in situ elemental analyses in clinopyroxene phenocrysts, integrated thermobarometry models, and bulk crystalline Hf, Nd, and Pb isotopic studies to reconstruct a key period of ancient eruptions of Mount Etna (Sicily), Europe’s largest, most active volcano. Trace element signatures recorded in clinopyroxene from 220 to 100 ka are consistent with derivation from a heterogeneous mantle of hydrated peridotite and ~10 % pyroxenite, also consistent with sources feeding recent Etna eruptions. Isotopic data from Mount Etna alkaline lava clinopyroxene, crystallised between 0.5 and 0.2 GPa, insignificantly vary from whole rock values, ruling out substantive assimilation of material during magma ascent from the onset of clinopyroxene fractionation through the mid-crust, storage, and eruption. Together, our results suggest that varying contributions of well-mixed hydrated peridotite and pyroxenite melts have been consistent features of magma assembly beneath Mt. Etna since the development of ancient alkaline centres.

Figures and Tables

Figure 1 (a) Ce contents of TSC cpx as a function of single-cpx pressure estimates (1σ uncertainty) superimposed on Etna stratigraphy (after Spilliaert et al., 2006). (b) Proportions of ancient Etna barometry from this study and previous work (cf. Supplementary Information, n = 287). (c) TSC cpx and 2001 eruption cpx (Viccaro et al., 2006) shown with Hyblean pyroxenite and peridotite cpx fields (Correale et al., 2012, and references therein). Isobaric cpx fractionation modelling for peridotite melt (solid lines) and pyroxenite melt (dashed lines) at 1.0 (black), 0.6 (grey), and 0.2 (blue) GPa performed using alphaMELTS (Smith and Asimow, 2005); conditions described in Supplementary Information. Fractionation of apatite, well known to incorporate REEs, is modelled in purple using the partitioning of Prowatke and Klemme (2006). Ol+cpx±opx+sp is present at the start of both trends, though olivine drops out at T < ~1100 °C for pyroxenite melt.

Figure 2 Ancient Etna cpx and WR data. (a) εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005. Hafnium isotopic values for Italian sediments (Conticelli et al., 2002; Brems et al., 2013) are calculated from Nd isotopic data and both cases following the seawater array (SA) and the terrestrial array (TA) of Vervoort et al. (2011) are shown. (b) 208Pb/204Pb vs. 206Pb/204Pb shown with OIB and mid-ocean ridge basalt (MORB) fields, historic Etna (Viccaro and Cristofolini, 2008) and Hyblean Plateau field from Trua et al. (1998). Italian crustal values from Conticelli et al. (2002). External reproducibility is conservatively set at 0.01 for 206Pb/204Pb and 0.02 for 208Pb/204Pb.

Figure 1 Figure 2

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Supplementary Figures and Tables

Figure S-1 Location of Timpe Santa Caterina outcrop on base map from GeoMapApp (http://www.geomapapp.org; Ryan et al., 2009). Major geologic features from Rosenbaum and Lister (2004). Stratigraphy based on Corsaro et al. (2002) with section base at sea level (0 m). Dates (*) from Gillot et al. (1994).

Figure S-2 Back scattered electron images of representative clinopyroxene grains from TSC lavas with laser ablation spots (Alfred University electron microprobe).

Table S-1 Electron microprobe analyses of TSC* clinopyroxene LA-ICP-MS laser spots. All iron reported as FeO. Operating conditions used at the University of Oregon (UO) and Massachusetts Institute of Technology (MIT) facilities were 15 keV accelerating voltage and 10 nA beam current, with all analyses using a focused beam of ~1 microns and 30 s count times. Data were reduced using the CITZAF correction procedure of Armstrong (1995). The few totals lower than 98 wt. % have been omitted. MIT JEOL JXA-8200 electron microprobe uncertainties (1σ) are calculated from the standard deviation of replicate analyses of the DJ35 diopside-jadeite glass standard and several points inferred from back scattered electron imaging to be from the same clinopyroxene crystal growth zone.
Analyses (wt. %) near laser spots TSC2_G1_3, TSC_G3_1, TSC2_G4_2, TSC7_G2_2, and TSC9_G5_2 totalled <98 wt. %. CaO abundances of the nearest same-grain spot were used to calibrate trace element concentrations (from TSC2_G1_2, TSC2_G3_2, TSC2_G4_1, TSC7_G2_1, and TSC9_G5_2, respectively).

Table S-2 Trace element data (ppm) collected by LA-ICP-MS at the University of New Hampshire.

Table S-3 Comparison of LA-ICP-MS repeat analyses of ML3B-G glass standard with reported literature values.

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

Table S-4 TSC clinopyroxene major element compositions (wt. %) along grain transects were analysed on the Massachusetts Institute of Technology (MIT) JEOL-JXA-8200 Superprobe. Uncertainty (2s) has been calculated from the standard deviation of replicate analyses of the DJ35 diopside-jadeite glass and ALP7 aluminous orthopyroxene standards, as well as several points inferred from back scattered electron imaging to be from the same clinopyroxene crystal growth zone: SiO2 (0.31), TiO2 (0.02), Al2O3 (0.07), FeO (0.08), MgO (0.11), MnO (0.01), CaO (0.30), Na2O (0.04), K (0.01), Cr2O3 (0.02).

Table S-5 Hf-Nd-Pb isotopic data for Timpe Santa Caterina whole rock (WR) and clinopyroxene (cpx) separates*. The uncertainties reported for Nd and Hf isotope ratios are internal 2 s.e. We use the values of external reproducibility as reported in the footnote to identify analytically resolvable WR-cpx disequilibrium discernable above the 2σ level.

Table S-6 Ranges of whole rock and clinopyroxene major and minor element compositions (wt. %) observed for the Timpe Santa Caterina flows studied.

Figure S-3 Clinopyroxene trace element evolution during isobaric fractionation of peridotite melt (green) and 10 % pyroxenite component melts (red) at 1.0, 0.6, and 0.2 GPa. Modelling sensitivity to starting composition is illustrated by including paths for melts with 5 % and 20 % pyroxenite component shown as blue and purple dotted lines, respectively.

Table S-4 Table S-5 Table S-6 Figure S-3

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Introduction


Volcanism began at Mount Etna, Europe’s largest and most active volcano, at ~0.5 Ma (Gillot et al., 1994

Gillot, P.Y., Kieffer, G., Romano, R. (1994) The evolution of Mount Etna in the light of potassium-argon dating. Acta Vulcanologica 5, 81–87.

), with ancient lavas now exposed around the perimeter of the modern-day edifice. Tholeiitic lavas were overlain by transitional and alkaline sequences starting at ~230 ka (Gillot et al., 1994

Gillot, P.Y., Kieffer, G., Romano, R. (1994) The evolution of Mount Etna in the light of potassium-argon dating. Acta Vulcanologica 5, 81–87.

; Branca and Del Carlo, 2004

Branca, S., Del Carlo, P. (2004) Eruptions of Mt. Etna during the past 3,200 Years: A revised compilation integrating the historical and stratigraphic records. In: Bonaccorso, A., Calvari, S., Coltelli, M., Del Negro, C., Falsaperla, S. (Eds.) Mt. Etna: Volcano Laboratory. American Geophysical Union, Washington, D.C., 1–27.

). Mt. Etna sits on the northern edge of the African plate at the European-African collision zone and the western hinge of escarpments dividing it from where the Ionian slab descends beneath the Aeolian arc (Fig. S-1, Supplementary Information). Volcanism has been attributed to the manifestation of mantle upwelling independent of, or in response to, a slab tear (e.g., Gasperini et al., 2002

Gasperini, D., Blichert-Toft, J., Bosch, D., Del Moro, A., Macera, P., Albarède, F. (2002) Upwelling of deep mantle material through a plate window; evidence from the geochemistry of Italian basaltic volcanics. Journal of Geophysical Research 107, 2367.

), subduction-related fluid-triggered melting (e.g., Armienti et al., 2007

Armienti, P., Tonarini, S., Innocenti, F., D'Orazio, M. (2007) Mount Etna pyroxene as tracer of petrogenetic processes and dynamics of the feeding system. In: Beccaluva, L., Bianchini, G., Wilson, M. (Eds.) Cenazoic volcanism in the Mediterranean Area. Geological Society of America Special Paper 418, 265–276.

and references therein) or enhanced decompression melting resulting from convective anomalies (Gvirtzman and Nur, 1999

Gvirtzman, Z., Nur, A. (1999) The formation of Mount Etna as the consequence of slab rollback. Nature 401, 782–785.

; Schellart, 2010

Schellart, W.P. (2010) Mount Etna–Iblean volcanism caused by rollback-induced upper mantle upwelling around the Ionian slab edge: An alternative to the plume model. Geology 38, 691–694.

).

Magmatic products of the early Etna centres, including those of the ancient alkali centres active at ~200–100 ka, bear mantle-derived isotopic signatures consistent with contributions from both enriched and depleted source components (Marty et al., 1994

Marty, B., Trull, T., Lussiez, P., Basile, I., Tanguy, J.-C. (1994) He, Ar, O, Sr and Nd isotope constraints on the origin and evolution of Mount Etna magmatism. Earth and Planetary Science Letters 126, 23–39.

; Tanguy et al., 1997

Tanguy, J.-C., Condomines, M., Kieffer, G. (1997) Evolution of the Mount Etna magma: Constraints on the present feeding system and eruptive mechanism. Journal of Volcanology and Geothermal Research 75, 221–250.

). Though more recent Etna volcanic products exhibit distinctive signs of assimilation in the form of elevated Sr isotopic values and large ion lithophile element enrichments (Tonarini et al., 1995

Tonarini, S., Armienti, P., D'Orazio, M., Innocenti, F., Pompilio, M., Petrini, R. (1995) Geochemical and isotopic monitoring of Mt. Etna 1989-1993 eruptive activity: bearing on the shallow feeding system. Journal of Volcanology and Geothermal Research 64, 95–115.

), the degree to which crustal contamination influenced early alkaline products is uncertain. Similarly, magmatic processes between mantle melting regions and shallow reservoirs supplying volcanic activity remain enigmatic. In this study, we combine clinopyroxene (cpx) barometry, trace element concentrations, and Pb, Hf, and Nd mineral-whole rock (WR) isotopic (dis)equilibria to constrain source compositions and differentiation depths of magmas feeding lavas erupted at Timpe Santa Caterina (TSC). The advantage of employing these three isotopic systems together lies in the coupling of the slowly diffusing Hf and Nd with the more rapidly diffusing Pb, thereby providing the potential to infer magma assembly processes prior to eruption during this early period.

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Sample Selection and Analytical Methods


Lavas at TSC encompass the whole ancient alkaline magmatism period at Etna, from 220 ka near sea level to likely <100 ka exposed atop the sea cliff (Gillot et al., 1994

Gillot, P.Y., Kieffer, G., Romano, R. (1994) The evolution of Mount Etna in the light of potassium-argon dating. Acta Vulcanologica 5, 81–87.

). Early trachybasaltic and basaltic flows, TSC-2 and TSC-3, are overlain by more alkalic basanites and phonotephritic lavas (TSC-7 and TSC-9). Flows selected for this study contain the most abundant large cpx from the TSC suite (Fig. S-2, Supplementary Information). Major and trace element and isotopic analytical details and data are provided in Tables S-1 to S-5 (Supplementary Information).

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Results and Discussion


Barometry. Observed cpx phenocrysts (>2 mm, large relative to other TSC lava phases) coupled with theoretical modelling of Etna compositions indicate early cpx crystallisation; hence cpx holds a potential record of pre-eruptive magma assembly processes (Armienti et al., 2009

Armienti, P., Gasperini, D., Perinelli, C., Putirka, K.D. (2009) A new model for estimating deep-level magma ascent rates from thermobarometry: an example from Mt. Etna and implications for deep-seated magma dehydration. Acta Vulcanologica 21, 145–158.

). Crystallisation temperatures and pressures, solved iteratively using a single-cpx thermometer and single-cpx barometer for hydrous systems (respectively, Eqs. 32d and 32b in Putirka, 2008

Putirka, K.D. (2008) Thermometers and barometers for volcanic systems. Reviews in Mineralogy and Geochemistry 69, 61–120.

), yielded temperatures of 1060–1175 °C and an average pressure of 0.34 ± 0.16 GPa (Fig. 1a,b). Thermobarometric model accuracy was evaluated using a literature dataset of >100 experimentally coexisting cpx-liquid pairs over a compositional range bracketing TSC lavas and cpx compositions (cf. Supplementary Information Table S-6 for equations, ranges, references, and selection criteria). As noted by Mollo et al. (2010)

Mollo, S., Del Gaudio, P., Ventura, G., Iezzi, G., Scarlato, P. (2010) Dependence of clinopyroxene composition on cooling rate in basaltic magmas: Implications for thermobarometry. Lithos 118, 302–312.

, single-cpx barometers can outperform liquid-based models for volatile-rich alkaline compositions. The single-cpx barometer for hydrous systems yields an average uncertainty of 0.17 versus 0.28 GPa for the cpx-liquid model of Putirka et al. (2003)

Putirka, K.D., Mikaelian, H., Ryerson, F., Shaw, H. (2003) New clinopyroxene-liquid thermometers for mafic, evolved, and volatile-bearing lava compositions, with applications to lavas from Tibet and the Snake River Plain, Idaho. American Mineralogist 88, 1542–1554.

for the compiled experiments, placing a lower bound of pressures recorded by TSC cpx at below 0.8 GPa, within the uppermost lithospheric mantle.

Crystallisation of TSC-2 and TSC-7 cpx generally occurred at depths centred around 0.5 GPa and 0.2–3 GPa, respectively (Fig. 1a), suggesting specific magma reservoir locations near the crystalline basement-granulite boundary and within the carbonate platform beneath Etna. More continuous polybaric crystallisation is apparent in TSC-3 and TSC-9. Combined with previous work on Etna lavas (see Supplementary Information), thermobarometry indicates that the bulk of ancient clinopyroxene phenocrysts crystallised between 0.5 and 0.2 GPa (Fig. 1b).


Figure 1 (a) Ce contents of TSC cpx as a function of single-cpx pressure estimates (1σ uncertainty) superimposed on Etna stratigraphy (after Spilliaert et al., 2006

Spilliaert, N., Allard, P., Métrich, N., Sobolev, A.V. (2006) Melt inclusion record of the conditions of ascent, degassing, and extrusion of volatile-rich alkali basalt during the powerful 2002 flank eruption of Mount Etna (Italy). Journal of Geophysical Research 111, B04203.

). (b) Proportions of ancient Etna barometry from this study and previous work (cf. Supplementary Information, n = 287). (c) TSC cpx and 2001 eruption cpx (Viccaro et al., 2006

Viccaro, M., Ferlito, C., Cortesogno, L., Cristofolini, R., Gaggero, L. (2006) Magma mixing during the 2001 event at Mount Etna (Italy): effects on the eruptive dynamics. Journal of Volcanology and Geothermal Research 149, 139–159.

) shown with Hyblean pyroxenite and peridotite cpx fields (Correale et al., 2012

Correale, A., Martelli, M., Paonita, A., Rizzo, A., Brusca, L., Scribano, V. (2012) New evidence of mantle heterogeneity beneath the Hyblean Plateau (southeast Sicily, Italy) as inferred from noble gases and geochemistry of ultramafic xenoliths. Lithos 132–133, 70–81.

, and references therein). Isobaric cpx fractionation modelling for peridotite melt (solid lines) and pyroxenite melt (dashed lines) at 1.0 (black), 0.6 (grey), and 0.2 (blue) GPa performed using alphaMELTS (Smith and Asimow, 2005

Smith, P.M., Asimow, P.D. (2005) Adiabat_1ph: A new public front-end to the MELTS, pMELTS, and pHMELTS models. Geochemistry Geophysics Geosystems 6, Q02004.

); conditions described in Supplementary Information. Fractionation of apatite, well known to incorporate REEs, is modelled in purple using the partitioning of Prowatke and Klemme (2006)

Prowatke, S., Klemme, S. (2006) Trace element partitioning between apatite and silicate melts. Geochimica et Cosmochimica Acta 70, 4513–4527.

. Ol+cpx±opx+sp is present at the start of both trends, though olivine drops out at T < ~1100 °C for pyroxenite melt.
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Heterogeneous mantle sources for ancient Etna. Clinopyroxene trace element concentrations, when coupled with single-cpx barometry pressure estimates, place constraints on magma source compositions and crustal mixing depths. Cerium, incompatible in all major TSC phases, functions as a fractionation proxy and indicator of magma evolution. Two distinct crystallisation paths are apparent in TSC cpx: trends characterised by high Y/La (TSC-2, TSC-7) and low Y/La (TSC-3, TSC-9) when linked with Ce (Fig. 1c). Clinopyroxene from the 2001 eruption also follow the low-Y/La trend, as do other known historic and recent Etna cpx (Viccaro et al., 2006

Viccaro, M., Ferlito, C., Cortesogno, L., Cristofolini, R., Gaggero, L. (2006) Magma mixing during the 2001 event at Mount Etna (Italy): effects on the eruptive dynamics. Journal of Volcanology and Geothermal Research 149, 139–159.

). Scarlato et al. (2014)

Scarlato, P., Mollo, S., Blundy, J.D., Iezzi, G., Tiepolo, M. (2014) The role of natural solidification paths on REE partitioning between clinopyroxene and melt. Bulletin of Volcanology 76, 810, doi: 10.1007/s00445-014-0810-1.

have documented preferential HREE incorporation into cpx relative to LREE as a function of cooling rate, but in TSC phenocrysts, HREE-like Y has either negative or no correlation with major element chemistry associated with elevated cooling rates (e.g., Na, AlIV, and Ti). Accordingly, we interpret the Y/La-Ce trends to reflect source characteristics beneath Etna over time rather than being a feature of crystallisation conditions.

Clinopyroxene grains record existence of magmas beneath Etna deriving from melting of both pyroxenitic and peridotitic mantle components. The source characterisation enabled by analysis of Y/La-Ce trends in Etna TSC cpx can also be used to evaluate the composition of cpx in pyroxenite and peridotite xenoliths from the nearby Hyblean Plateau (Fig. 1c). Clinopyroxene from Hyblean pyroxenite xenoliths plot along the high-Y/La TSC trend (Fig. 1c), which is reproduced with a primary melt generated by a heterogeneous source of 10 % dry pyroxenite and 90 % hydrated peridotite in which ~10 % of each lithology melts and mixes at 1.5 GPa. Figure S-3 shows hypothetical source compositions with up to 20 % pyroxenite to constrain model sensitivity (Supplementary Information). These lithologies, similar to those determined by Correale et al. (2014)

Correale, A., Paonita, A., Martelli, M., Rizzo, A., Rotolo, S.G., Corsaro, R.A., Di Renzo, V. (2014) A two-component mantle source feeding Mt.Etna magmatism: Insights from the geochemistry of primitive magmas. Lithos 184–187, 243–258.

modelling trace element systematics in primitive Etna WR samples <15 ka, are distinct from peridotitic cpx from the nearby Hyblean plateau that fall below the low-Y/La trend. Low Y/La in cpx may result from either a hydrated peridotite source or a more evolved melt of the mixed pyroxenite source following apatite saturation.

Isotopic (dis)equilibria. Most Etna mineral-WR pair isotopic work has focused on the Sr and Nd systems in recent lavas (e.g., Tonarini et al., 1995

Tonarini, S., Armienti, P., D'Orazio, M., Innocenti, F., Pompilio, M., Petrini, R. (1995) Geochemical and isotopic monitoring of Mt. Etna 1989-1993 eruptive activity: bearing on the shallow feeding system. Journal of Volcanology and Geothermal Research 64, 95–115.

), which generally exhibit more radiogenic Sr and less radiogenic Nd than ancient lavas. Within recent eruptive episodes, marked increases in WR 87Sr/86Sr are often accompanied by 87Sr/86Sr WR-cpx disequilibria (e.g., 0.70348 cpx core values accompanied by 0.70362 WR values in 2001 eruptives; Armienti et al., 2007

Armienti, P., Tonarini, S., Innocenti, F., D'Orazio, M. (2007) Mount Etna pyroxene as tracer of petrogenetic processes and dynamics of the feeding system. In: Beccaluva, L., Bianchini, G., Wilson, M. (Eds.) Cenazoic volcanism in the Mediterranean Area. Geological Society of America Special Paper 418, 265–276.

).

Our approach employing coupled Hf, Nd, and Pb isotopic signatures in ancient volcanics brings three distinct chemical affinities to bear on determining magma assembly, as recorded in cpx trace elements, at depths constrained by thermobarometry. As refractory elements diffusing slowly in clinopyroxene (cf. Van Orman et al., 2001

Van Orman, J.A., Grove, T.L., Shimizu, N. (2001) Rare earth element diffusion in diopside: influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates. Contributions to Mineralogy and Petrology 141, 687–703.

), Nd and Hf may be expected to retain isotopic signatures from early crystallisation depths and exhibit large isotopic disequilibria with hosting magmas subject to mixing with recharging, or assimilating magmas, carrying isotopically distinctive compositions immediately prior to eruption. In contrast, Pb diffuses relatively rapidly, making Pb isotope systematics an especially promising approach for placing constraints on magma residence times within the crust.

Since each separate cpx analysis represents digestion of multiple grains likely crystallised at different depths, reported isotopic values reflect an average over the polybaric cpx crystallisation history. However, sluggish Nd and Hf re-equilibration will manifest itself as WR-cpx disequilibria in cases of late-stage incorporation of any volumetrically significant isotopically distinct magma during the final stages of magma assembly.

Neodymium and Hf isotopic compositions (Fig. 2a) of TSC cpx and WR demonstrate they are insignificantly distinctive at the 2σ level. However, it is notable that all cpx have slightly more enriched Nd isotopic signatures that trend toward those of continental values. This could result from a recharge process of fresher mantle-derived material that drives eruption. Late-stage shallow contamination, by contrast, would impart enriched crustal signatures to the WR, presumably after cpx phenocryst formation. Though Hf and Nd isotopic data for sedimentary units directly beneath Etna are unavailable for comparison with cpx and WR values, Sicilian beach sand εNd derived from the western extension of sedimentary units underlying Etna and crustal rocks of south and central Italy are all considerably more enriched (Fig. 2a; εNd -10.3 to -16.0, Conticelli et al., 2002

Conticelli, S., D'Antonio, M., Pinarelli, L., Civetta, L. (2002) Source contamination and mantle heterogeneity in the genesis of Italian potassic and ultrapotassic volcanic rocks: Sr‚ Nd‚ Pb isotope data from Roman Province and Southern Tuscany. Mineralogy and Petrology 74,189–222.

; Brems et al., 2013

Brems, D., Ganio, M., Latruwe, K., Balcaen, L., Carremans, M., Gimeno, D., Silvestri, A., Vanhaecke, F., Muchez, P., Degryse, P. (2013) Isotopes on the beach, part 2: neodymium isotopic analysis for the provenancing of Roman glass-making. Archaeometry 55, 449–464.

). Such large differences make it unlikely that crustal sediments contributed to the Hf and Nd isotopic compositions observed in TSC cpx and WR materials. Rather, we infer that the isotopic signatures of these magmas were locked in at pressures corresponding, at minimum, to early cpx crystallisation at mid-crustal pressures of 0.5–0.2 GPa.


Figure 2 Ancient Etna cpx and WR data. (a) εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003

Lassiter, J.C., Blichert-Toft, J., Hauri, E.H., Barsczus, H.G. (2003) Isotope and trace element variations in lavas from Raivavae and Rapa, Cook‚ Austral islands: constraints on the nature of HIMU- and EM-mantle and the origin of mid-plate volcanism in French Polynesia. Chemical Geology 202, 115–138.

; Stracke et al., 2003

Stracke, A., Bizimis, M., Salters, V.J.M. (2003) Recycling oceanic crust: Quantitative constraints. Geochemistry Geophysics Geosystems 4, 8003.

; Gaffney et al., 2004

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; Huang et al., 2005

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; Xu et al., 2007

Xu, G., Frey, F.A., Clague, D.A., Abouchami, W., Blichert-Toft, J., Cousens, B., Weisler, M. (2007) Geochemical characteristics of West Molokai shield-and postshield-stage lavas: Constraints on Hawaiian plume models. Geochemistry Geophysics Geosystems 8, Q08G21.

; Sims et al., 2008

Sims, K.W.W., Blichert-Toft, J., Kyle, P.R., Pichat, S., Gauthier, P.-J., Blusztajn, J., Kelly, P., Ball, L., Layne, G. (2008) A Sr, Nd, Hf, and Pb isotope perspective on the genesis and long-term evolution of alkaline magmas from Erebus volcano, Antarctica. Journal of Volcanology and Geothermal Research 177, 606–618.

; 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.

; Yamasaki et al., 2009

Yamasaki, S., Kani, T., Hanan, B.B., Tagami, T. (2009) Isotopic geochemistry of Hualalai shield-stage tholeiitic basalts from submarine North Kona region, Hawaii. Journal of Volcanology and Geothermal Research 185, 223–230.

; Garcia et al., 2010

Garcia, M.O., Swinnard, L., Weis, D., Greene, A.R., Tagami, T., Sano, H., Gandy, C.E. (2010) Petrology, geochemistry and geochronology of Kaua ‘i Lavas over 4· 5 Myr: Implications for the origin of rejuvenated volcanism and the evolution of the Hawaiian plume. Journal of Petrology 51, 1507–1540.

; Peate et al., 2010

Peate, D.W., Breddam, K., Baker, J.A., Kurz, M.D., Barker, A.K., Prestvik, T., Grassineau, N., Skovgaard, A.C. (2010) Compositional characteristics and spatial distribution of enriched Icelandic mantle components. Journal of Petrology 51, 1447–1475.

; Chekol et al., 2011

Chekol, T.A., Kobayashi, K., Yokoyama, T., Sakaguchi, C., Nakamura, E. (2011) Timescales of magma differentiation from basalt to andesite beneath Hekla Volcano, Iceland: Constraints from U-series disequilibria in lavas from the last quarter-millennium flows. Geochimica et Cosmochimica Acta 75, 256–283.

; Salters et al., 2011

Salters, V.J.M., Mallick, S., Hart, S.R., Langmuir, C.E., Stracke, A. (2011) Domains of depleted mantle: New evidence from hafnium and neodymium isotopes. Geochemistry Geophysics Geosystems 12, Q08001.

; Viccaro et al., 2011

Viccaro, M., Nicotra, E., Millar, I.L., Cristofolini, R. (2011) The magma source at Mount Etna volcano: Perspectives from the Hf isotope composition of historic and recent lavas. Chemical Geology 281, 343–351.

); mantle components from Zindler and Hart, 1986

Zindler, A., Hart, S. (1986) Chemical geodynamics. Annual Review of Earth and Planetary Sciences 14, 493–571.

; Salters and White, 1998

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

; Workman et al., 2004

Workman, R.K., Hart, S.R., Jackson, M., Regelous, M., Farley, K.A., Blusztajn, J., Kurz, M., Staudigel, H. (2004) Recycled metasomatized lithosphere as the origin of the Enriched Mantle II (EM2) end-member: Evidence from the Samoan Volcanic Chain. Geochemistry Geophysics Geosystems 5, Q04008.

; Stracke et al., 2005

Stracke, A., Hofmann, A.W., Hart, S.R. (2005) FOZO, HIMU, and the rest of the mantle zoo. Geochemistry Geophysics Geosystems 6, Q05007.

; Workman and Hart, 2005

Workman, R.K., Hart, S.R. (2005) Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters 231, 53–72.

. Hafnium isotopic values for Italian sediments (Conticelli et al., 2002

Conticelli, S., D'Antonio, M., Pinarelli, L., Civetta, L. (2002) Source contamination and mantle heterogeneity in the genesis of Italian potassic and ultrapotassic volcanic rocks: Sr‚ Nd‚ Pb isotope data from Roman Province and Southern Tuscany. Mineralogy and Petrology 74,189–222.

; Brems et al., 2013

Brems, D., Ganio, M., Latruwe, K., Balcaen, L., Carremans, M., Gimeno, D., Silvestri, A., Vanhaecke, F., Muchez, P., Degryse, P. (2013) Isotopes on the beach, part 2: neodymium isotopic analysis for the provenancing of Roman glass-making. Archaeometry 55, 449–464.

) are calculated from Nd isotopic data and both cases following the seawater array (SA) and the terrestrial array (TA) of Vervoort et al. (2011)

Vervoort, J.D., Plank, T., Prytulak, J. (2011) The Hf-Nd isotopic composition of marine sediments. Geochimica et Cosmochimica Acta 75, 5903–5926.

are shown. (b) 208Pb/204Pb vs. 206Pb/204Pb shown with OIB and mid-ocean ridge basalt (MORB) fields, historic Etna (Viccaro and Cristofolini, 2008

Viccaro, M., Cristofolini, R. (2008) Nature of mantle heterogeneity and its role in the short-term geochemical and volcanological evolution of Mt. Etna (Italy). Lithos 105, 272–288.

) and Hyblean Plateau field from Trua et al. (1998)

Trua, T., Esperança, S., Mazzuoli, R. (1998) The evolution of the lithospheric mantle along the N. African Plate: geochemical and isotopic evidence from the tholeiitic and alkaline volcanic rocks of the Hyblean plateau, Italy. Contributions to Mineralogy and Petrology 131, 307–322.

. Italian crustal values from Conticelli et al. (2002)

Conticelli, S., D'Antonio, M., Pinarelli, L., Civetta, L. (2002) Source contamination and mantle heterogeneity in the genesis of Italian potassic and ultrapotassic volcanic rocks: Sr‚ Nd‚ Pb isotope data from Roman Province and Southern Tuscany. Mineralogy and Petrology 74,189–222.

. External reproducibility is conservatively set at 0.01 for 206Pb/204Pb and 0.02 for 208Pb/204Pb.
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Constraints on mantle mixing processes. In spite of barometric model uncertainties, sites of cpx crystallisation (shallow crust vs. lower crust/mantle) can be readily distinguished by the barometry and thus provide meaningful stratigraphic context for cpx isotopic values. The lack of significant disequilibrium can be explained by magma sources feeding Etna during the period of ancient alkaline eruptive activity being either broadly isotopically homogeneous or well mixed before eruption. The few reported WR-cpx pairs from 15–30 ka (Valle del Bove sequence; D'Orazio et al., 1997

D'Orazio, M., Tonarini, S., Innocenti, F., Pompilio, M. (1997) Northern Valle del Bove volcanic succession (Mt. Etna, Sicily): petrography, geochemistry and Sr-Nd isotope data. Acta Vulcanologica 9, 73–86.

) show corresponding Sr and Nd isotopic equilibria (isotopic differences <0.00002 and <0.00001, respectively) and results here extend this phenomenon back an additional 200 ka.

The interpretation of limited mixing is further supported by the observed equilibrium in three of the TSC lavas between cpx and WR Pb isotopic signatures (Fig. 2b). Only one WR-cpx pair (TSC-7) exhibits isotopic disequilibrium in the Pb isotope system just outside the range of external reproducibility. Limited crustal storage time implied by Pb isotopic cpx-WR equilibria also bolsters trace element records of crystallisation from heterogeneously sourced magmas being largely preserved in this system. Trace element modelling of sources is particularly valuable in cases where source isotopic signatures are relatively well homogenised.

The restricted isotopic range of TSC cpx and WR values contrasts sharply with the variety of Pb isotopic signatures observed for plagioclase-rich and magnetic splits of a finer-grained 260 ka Etna tholeiite (SdV-1) reported by Bryce and DePaolo (2004)

Bryce, J.G., DePaolo, D.J. (2004) Pb isotopic heterogeneity in basaltic phenocrysts. Geochimica et Cosmochimica Acta 68, 4453–4468.

and olivine-hosted melt inclusions from recent (2002) eruptions (Rose-Koga et al., 2012

Rose-Koga, E.F., Koga, K.T., Schiano, P., Le Voyer, M., Shimizu, N., Whitehouse, M.J., Clocchiatti, R. (2012) Mantle source heterogeneity for South Tyrrhenian magmas revealed by Pb isotopes and halogen contents of olivine-hosted melt inclusions. Chemical Geology 334, 266–279.

). Possible explanations include that these lavas may sample geographically different magma supplies or derive from magmas experiencing additional mixing immediately prior to eruption, as inferred from olivine in recent lavas (Kahl et al., 2011

Kahl, M., Chakraborty, S., Costa, F., Pompilio, M. (2011) Dynamic plumbing system beneath volcanoes revealed by kinetic modeling, and the connection to monitoring data: An example from Mt. Etna. Earth and Planetary Science Letters 308, 11–22.

). Variable Pb isotopic compositions in olivine-hosted melt inclusions could signify that minute amounts of isotopically distinct melts are simply insufficiently abundant to change the “deep”, dominant isotopic signal locked into cpx.

Lack of Hf-Nd-Pb isotopic disequilibria in ancient TSC lavas between cpx-WR pairs indicates that any mixing of isotopically distinct magmas supplying ancient Etna eruptions occurred at depths preceding cpx crystallisation. Melts then rose to the surface without significant assimilation in (and associated heat exchange with) shallow reservoirs.

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Conclusions


Thermobarometrically controlled elemental and isotopic analyses of clinopyroxene provide a means to reconstruct ancient magma assembly processes at Mt. Etna. Single-crystal cpx barometry places most phenocryst crystallisation within the mid-crust and permits distinction between deep and shallow processes when coupled with trace element and isotopic data. In situ trace element data from cpx allow for the assessment of pyroxenite vs. peridotite contributions to Etna magmas. Chemical signatures apparent in these ancient lavas as well as in modern products suggest that hydrated peridotite has been an important component of the magma source region over the history of this volcano. The present dataset further supports the interpretation that observed isotopic systematics in ancient Etna lavas resulted from mixing between depleted and enriched mantle sources, with volatile-bearing peridotite and pyroxenite components preferentially melting to generate volatile-rich ancient alkaline volcanism. Hf-Nd-Pb isotopic equilibria between TSC WR and cpx are consistent with a model of an ancient Etna plumbing system wherein melts were homogenised below mid-crustal depths and then rapidly transported to the surface without substantial assimilation of crustal material at pressures lower than 0.5 GPa. More extensive combinations of bulk isotopic stratigraphy with mineral barometric and trace element modelling as applied here are expected to afford opportunities to reconstruct the longevity of magmatic plumbing systems and deconvolve distinctive magma source regions feeding Mt. Etna through time.

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Acknowledgements


We thank Nilanjan Chatterjee, Julie Chouinard, Philippe Télouk, and Gerald Wynick for technical assistance, the Alfred University Center for Advanced Ceramic Technology (CACT), and Wendy Bohrson for comments on an earlier version of the manuscript. We appreciate thoughtful suggestions of Pietro Armienti, two anonymous reviewers, and the editorial handling by Bruce Watson, all of which improved the quality of our manuscript. Financial support from NSF grant EAR-1057611 to JGB and SAM, the UNH Undergraduate Research Opportunities Program to MM, and the French Agence Nationale de la Recherche (grant ANR-10-BLANC-0603 M&Ms – Mantle Melting – Measurements, Models, Mechanisms) to JBT is gratefully acknowledged.

Editor: Bruce Watson

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References



Armienti, P., Tonarini, S., Innocenti, F., D'Orazio, M. (2007) Mount Etna pyroxene as tracer of petrogenetic processes and dynamics of the feeding system. In: Beccaluva, L., Bianchini, G., Wilson, M. (Eds.) Cenazoic volcanism in the Mediterranean Area. Geological Society of America Special Paper 418, 265–276.
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Volcanism has been attributed to the manifestation of mantle upwelling independent of, or in response to, a slab tear (e.g., Gasperini et al., 2002), subduction-related fluid-triggered melting (e.g., Armienti et al., 2007 and references therein) or enhanced decompression melting resulting from convective anomalies (Gvirtzman and Nur, 1999; Schellart, 2010).
View in article
Most Etna mineral-WR pair isotopic work has focused on the Sr and Nd systems in recent lavas (e.g., Tonarini et al., 1995; Armienti et al., 2007), which generally exhibit more radiogenic Sr and less radiogenic Nd than ancient lavas.
View in article
Within recent eruptive episodes, marked increases in WR 87Sr/86Sr are often accompanied by 87Sr/86Sr WR-cpx disequilibria (e.g., 0.70348 cpx core values accompanied by 0.70362 WR values in 2001 eruptives; Armienti et al., 2007).
View in article


Armienti, P., Gasperini, D., Perinelli, C., Putirka, K.D. (2009) A new model for estimating deep-level magma ascent rates from thermobarometry: an example from Mt. Etna and implications for deep-seated magma dehydration. Acta Vulcanologica 21, 145–158.
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Observed cpx phenocrysts (>2 mm, large relative to other TSC lava phases) coupled with theoretical modelling of Etna compositions indicate early cpx crystallisation; hence cpx holds a potential record of pre-eruptive magma assembly processes (Armienti et al. 2009).
View in article


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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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
View in article


Branca, S., Del Carlo, P. (2004) Eruptions of Mt. Etna during the past 3,200 Years: A revised compilation integrating the historical and stratigraphic records. In: Bonaccorso, A., Calvari, S., Coltelli, M., Del Negro, C., Falsaperla, S. (Eds.) Mt. Etna: Volcano Laboratory. American Geophysical Union, Washington, D.C., 1–27.
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Tholeiitic lavas were overlain by transitional and alkaline sequences starting at ~230 ka (Gillot et al., 1994; Branca and Del Carlo, 2004).
View in article


Brems, D., Ganio, M., Latruwe, K., Balcaen, L., Carremans, M., Gimeno, D., Silvestri, A., Vanhaecke, F., Muchez, P., Degryse, P. (2013) Isotopes on the beach, part 2: neodymium isotopic analysis for the provenancing of Roman glass-making. Archaeometry 55, 449–464.
Show in context

Though Hf and Nd isotopic data for sedimentary units directly beneath Etna are unavailable for comparison with cpx and WR values, Sicilian beach sand εNd derived from the western extension of sedimentary units underlying Etna and crustal rocks of south and central Italy are all considerably more enriched (Fig. 2a; εNd -10.3 to -16.0, Conticelli et al., 2002; Brems et al., 2013).
View in article
Figure 2 [...] Hafnium isotopic values for Italian sediments (Conticelli et al., 2002; Brems et al., 2013) are calculated from Nd isotopic data and both cases following the seawater array (SA) and the terrestrial array (TA) of Vervoort et al. (2011) are shown.
View in article


Bryce, J.G., DePaolo, D.J. (2004) Pb isotopic heterogeneity in basaltic phenocrysts. Geochimica et Cosmochimica Acta 68, 4453–4468.
Show in context

The restricted isotopic range of TSC cpx and WR values contrasts sharply with the variety of Pb isotopic signatures observed for plagioclase-rich and magnetic splits of a finer-grained 260 ka Etna tholeiite (SdV-1) reported by Bryce and DePaolo (2004) and olivine-hosted melt inclusions from recent (2002) eruptions (Rose-Koga et al., 2012).
View in article


Chekol, T.A., Kobayashi, K., Yokoyama, T., Sakaguchi, C., Nakamura, E. (2011) Timescales of magma differentiation from basalt to andesite beneath Hekla Volcano, Iceland: Constraints from U-series disequilibria in lavas from the last quarter-millennium flows. Geochimica et Cosmochimica Acta 75, 256–283.
Show in context

Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
View in article


Conticelli, S., D'Antonio, M., Pinarelli, L., Civetta, L. (2002) Source contamination and mantle heterogeneity in the genesis of Italian potassic and ultrapotassic volcanic rocks: Sr‚ Nd‚ Pb isotope data from Roman Province and Southern Tuscany. Mineralogy and Petrology 74,189–222.
Show in context

Though Hf and Nd isotopic data for sedimentary units directly beneath Etna are unavailable for comparison with cpx and WR values, Sicilian beach sand εNd derived from the western extension of sedimentary units underlying Etna and crustal rocks of south and central Italy are all considerably more enriched (Fig. 2a; εNd -10.3 to -16.0, Conticelli et al., 2002; Brems et al., 2013).
View in article
Figure 2 [...] Hafnium isotopic values for Italian sediments (Conticelli et al., 2002; Brems et al., 2013) are calculated from Nd isotopic data and both cases following the seawater array (SA) and the terrestrial array (TA) of Vervoort et al. (2011) are shown.
View in article
Figure 2 [...] Italian crustal values from Conticelli et al. (2002).
View in article


Correale, A., Martelli, M., Paonita, A., Rizzo, A., Brusca, L., Scribano, V. (2012) New evidence of mantle heterogeneity beneath the Hyblean Plateau (southeast Sicily, Italy) as inferred from noble gases and geochemistry of ultramafic xenoliths. Lithos 132–133, 70–81.
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Figure 1 [...] (c) TSC cpx and 2001 eruption cpx (Viccaro et al., 2006) shown with Hyblean pyroxenite and peridotite cpx fields (Correale et al., 2012, and references therein).
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Correale, A., Paonita, A., Martelli, M., Rizzo, A., Rotolo, S.G., Corsaro, R.A., Di Renzo, V. (2014) A two-component mantle source feeding Mt.Etna magmatism: Insights from the geochemistry of primitive magmas. Lithos 184–187, 243–258.
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These lithologies, similar to those determined by Correale et al. (2014) modelling trace element systematics in primitive Etna WR samples <15 ka, are distinct from peridotitic cpx from the nearby Hyblean plateau that fall below the low-Y/La trend.
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D'Orazio, M., Tonarini, S., Innocenti, F., Pompilio, M. (1997) Northern Valle del Bove volcanic succession (Mt. Etna, Sicily): petrography, geochemistry and Sr-Nd isotope data. Acta Vulcanologica 9, 73–86.
Show in context

The few reported WR-cpx pairs from 15–30 ka (Valle del Bove sequence; D'Orazio et al., 1997) show corresponding Sr and Nd isotopic equilibria (isotopic differences <0.00002 and <0.00001, respectively) and results here extend this phenomenon back an additional 200 ka.
View in article


Gaffney, A.M., Nelson, B.K., Blichert-Toft, J. (2004) Geochemical constraints on the role of oceanic lithosphere in intra-volcano heterogeneity at West Maui, Hawaii. Journal of Petrology 45, 1663–1687.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
View in article


Garcia, M.O., Swinnard, L., Weis, D., Greene, A.R., Tagami, T., Sano, H., Gandy, C.E. (2010) Petrology, geochemistry and geochronology of Kaua ‘i Lavas over 4· 5 Myr: Implications for the origin of rejuvenated volcanism and the evolution of the Hawaiian plume. Journal of Petrology 51, 1507–1540.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
View in article


Gasperini, D., Blichert-Toft, J., Bosch, D., Del Moro, A., Macera, P., Albarède, F. (2002) Upwelling of deep mantle material through a plate window; evidence from the geochemistry of Italian basaltic volcanics. Journal of Geophysical Research 107, 2367.
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Volcanism has been attributed to the manifestation of mantle upwelling independent of, or in response to, a slab tear (e.g., Gasperini et al., 2002), subduction-related fluid-triggered melting (e.g., Armienti et al., 2007 and references therein) or enhanced decompression melting resulting from convective anomalies (Gvirtzman and Nur, 1999; Schellart, 2010).
View in article


Gillot, P.Y., Kieffer, G., Romano, R. (1994) The evolution of Mount Etna in the light of potassium-argon dating. Acta Vulcanologica 5, 81–87.
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Volcanism began at Mount Etna, Europe’s largest and most active volcano, at ~0.5 Ma (Gillot et al., 1994), with ancient lavas now exposed around the perimeter of the modern-day edifice.
View in article
Tholeiitic lavas were overlain by transitional and alkaline sequences starting at ~230 ka (Gillot et al., 1994; Branca and Del Carlo, 2004).
View in article
Lavas at TSC encompass the whole ancient alkaline magmatism period at Etna, from 220 ka near sea level to likely <100 ka exposed atop the sea cliff (Gillot et al., 1994).
View in article


Gvirtzman, Z., Nur, A. (1999) The formation of Mount Etna as the consequence of slab rollback. Nature 401, 782–785.
Show in context

Volcanism has been attributed to the manifestation of mantle upwelling independent of, or in response to, a slab tear (e.g., Gasperini et al., 2002), subduction-related fluid-triggered melting (e.g., Armienti et al., 2007 and references therein) or enhanced decompression melting resulting from convective anomalies (Gvirtzman and Nur, 1999; Schellart, 2010).
View in article


Huang, S., Frey, F.A., Blichert-Toft, J., Fodor, R.V., Bauer, G.R., Xu, G. (2005) Enriched components in the Hawaiian plume: Evidence from Kahoolawe Volcano, Hawaii. Geochemistry Geophysics Geosystems 6, Q11006.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
View in article


Kahl, M., Chakraborty, S., Costa, F., Pompilio, M. (2011) Dynamic plumbing system beneath volcanoes revealed by kinetic modeling, and the connection to monitoring data: An example from Mt. Etna. Earth and Planetary Science Letters 308, 11–22.
Show in context

Possible explanations include that these lavas may sample geographically different magma supplies or derive from magmas experiencing additional mixing immediately prior to eruption, as inferred from olivine in recent lavas (Kahl et al., 2011).
View in article


Lassiter, J.C., Blichert-Toft, J., Hauri, E.H., Barsczus, H.G. (2003) Isotope and trace element variations in lavas from Raivavae and Rapa, Cook‚ Austral islands: constraints on the nature of HIMU- and EM-mantle and the origin of mid-plate volcanism in French Polynesia. Chemical Geology 202, 115–138.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
View in article


Marty, B., Trull, T., Lussiez, P., Basile, I., Tanguy, J.-C. (1994) He, Ar, O, Sr and Nd isotope constraints on the origin and evolution of Mount Etna magmatism. Earth and Planetary Science Letters 126, 23–39.
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Magmatic products of the early Etna centres, including those of the ancient alkali centres active at ~200–100 ka, bear mantle-derived isotopic signatures consistent with contributions from both enriched and depleted source components (Marty et al., 1994; Tanguy et al., 1997).
View in article


Mollo, S., Del Gaudio, P., Ventura, G., Iezzi, G., Scarlato, P. (2010) Dependence of clinopyroxene composition on cooling rate in basaltic magmas: Implications for thermobarometry. Lithos 118, 302–312.
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As noted by Mollo et al. (2010), single-cpx barometers can outperform liquid-based models for volatile-rich alkaline compositions.
View in article


Peate, D.W., Breddam, K., Baker, J.A., Kurz, M.D., Barker, A.K., Prestvik, T., Grassineau, N., Skovgaard, A.C. (2010) Compositional characteristics and spatial distribution of enriched Icelandic mantle components. Journal of Petrology 51, 1447–1475.
Show in context

Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
View in article


Prowatke, S., Klemme, S. (2006) Trace element partitioning between apatite and silicate melts. Geochimica et Cosmochimica Acta 70, 4513–4527.
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Figure 1 [...] Fractionation of apatite, well known to incorporate REEs, is modelled in purple using the partitioning of Prowatke and Klemme (2006).
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Putirka, K.D. (2008) Thermometers and barometers for volcanic systems. Reviews in Mineralogy and Geochemistry 69, 61–120.
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Crystallisation temperatures and pressures, solved iteratively using a single-cpx thermometer and single-cpx barometer for hydrous systems (respectively, Eqs. 32d and 32b in Putirka, 2008), yielded temperatures of 1060–1175 °C and an average pressure of 0.34 ± 0.16 GPa (Fig. 1a,b).
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Putirka, K.D., Mikaelian, H., Ryerson, F., Shaw, H. (2003) New clinopyroxene-liquid thermometers for mafic, evolved, and volatile-bearing lava compositions, with applications to lavas from Tibet and the Snake River Plain, Idaho. American Mineralogist 88, 1542–1554.
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The single-cpx barometer for hydrous systems yields an average uncertainty of 0.17 versus 0.28 GPa for the cpx-liquid model of Putirka et al. (2003) for the compiled experiments, placing a lower bound of pressures recorded by TSC cpx at below 0.8 GPa, within the uppermost lithospheric mantle.
View in article


Rose-Koga, E.F., Koga, K.T., Schiano, P., Le Voyer, M., Shimizu, N., Whitehouse, M.J., Clocchiatti, R. (2012) Mantle source heterogeneity for South Tyrrhenian magmas revealed by Pb isotopes and halogen contents of olivine-hosted melt inclusions. Chemical Geology 334, 266–279.
Show in context

The restricted isotopic range of TSC cpx and WR values contrasts sharply with the variety of Pb isotopic signatures observed for plagioclase-rich and magnetic splits of a finer-grained 260 ka Etna tholeiite (SdV-1) reported by Bryce and DePaolo (2004) and olivine-hosted melt inclusions from recent (2002) eruptions (Rose-Koga et al., 2012).
View in article


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 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Salters, V.J.M., Mallick, S., Hart, S.R., Langmuir, C.E., Stracke, A. (2011) Domains of depleted mantle: New evidence from hafnium and neodymium isotopes. Geochemistry Geophysics Geosystems 12, Q08001.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Scarlato, P., Mollo, S., Blundy, J.D., Iezzi, G., Tiepolo, M. (2014) The role of natural solidification paths on REE partitioning between clinopyroxene and melt. Bulletin of Volcanology 76, 810, doi: 10.1007/s00445-014-0810-1.
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Scarlato et al. (2014) have documented preferential HREE incorporation into cpx relative to LREE as a function of cooling rate, but in TSC phenocrysts, HREE-like Y has either negative or no correlation with major element chemistry associated with elevated cooling rates (e.g., Na, AlIV, and Ti).
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Schellart, W.P. (2010) Mount Etna–Iblean volcanism caused by rollback-induced upper mantle upwelling around the Ionian slab edge: An alternative to the plume model. Geology 38, 691–694.
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Volcanism has been attributed to the manifestation of mantle upwelling independent of, or in response to, a slab tear (e.g., Gasperini et al., 2002), subduction-related fluid-triggered melting (e.g., Armienti et al., 2007 and references therein) or enhanced decompression melting resulting from convective anomalies (Gvirtzman and Nur, 1999; Schellart, 2010).
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Smith, P.M., Asimow, P.D. (2005) Adiabat_1ph: A new public front-end to the MELTS, pMELTS, and pHMELTS models. Geochemistry Geophysics Geosystems 6, Q02004.
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Figure 1 [...] Isobaric cpx fractionation modelling for peridotite melt (solid lines) and pyroxenite melt (dashed lines) at 1.0 (black), 0.6 (grey), and 0.2 (blue) GPa performed using alphaMELTS (Smith and Asimow, 2005); conditions described in Supplementary Information.
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Sims, K.W.W., Blichert-Toft, J., Kyle, P.R., Pichat, S., Gauthier, P.-J., Blusztajn, J., Kelly, P., Ball, L., Layne, G. (2008) A Sr, Nd, Hf, and Pb isotope perspective on the genesis and long-term evolution of alkaline magmas from Erebus volcano, Antarctica. Journal of Volcanology and Geothermal Research 177, 606–618.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Spilliaert, N., Allard, P., Métrich, N., Sobolev, A.V. (2006) Melt inclusion record of the conditions of ascent, degassing, and extrusion of volatile-rich alkali basalt during the powerful 2002 flank eruption of Mount Etna (Italy). Journal of Geophysical Research 111, B04203.
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Figure 1 (a) Ce contents of TSC cpx as a function of single-cpx pressure estimates (1σ uncertainty) superimposed on Etna stratigraphy (after Spilliaert et al., 2006).
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Stracke, A., Bizimis, M., Salters, V.J.M. (2003) Recycling oceanic crust: Quantitative constraints. Geochemistry Geophysics Geosystems 4, 8003.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Stracke, A., Hofmann, A.W., Hart, S.R. (2005) FOZO, HIMU, and the rest of the mantle zoo. Geochemistry Geophysics Geosystems 6, Q05007.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Tanguy, J.-C., Condomines, M., Kieffer, G. (1997) Evolution of the Mount Etna magma: Constraints on the present feeding system and eruptive mechanism. Journal of Volcanology and Geothermal Research 75, 221–250.
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Magmatic products of the early Etna centres, including those of the ancient alkali centres active at ~200–100 ka, bear mantle-derived isotopic signatures consistent with contributions from both enriched and depleted source components (Marty et al., 1994; Tanguy et al., 1997).
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Tonarini, S., Armienti, P., D'Orazio, M., Innocenti, F., Pompilio, M., Petrini, R. (1995) Geochemical and isotopic monitoring of Mt. Etna 1989-1993 eruptive activity: bearing on the shallow feeding system. Journal of Volcanology and Geothermal Research 64, 95–115.
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Though more recent Etna volcanic products exhibit distinctive signs of assimilation in the form of elevated Sr isotopic values and large ion lithophile element enrichments (Tonarini et al., 1995), the degree to which crustal contamination influenced early alkaline products is uncertain.
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Most Etna mineral-WR pair isotopic work has focused on the Sr and Nd systems in recent lavas (e.g., Tonarini et al., 1995; Armienti et al., 2007), which generally exhibit more radiogenic Sr and less radiogenic Nd than ancient lavas.
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Trua, T., Esperança, S., Mazzuoli, R. (1998) The evolution of the lithospheric mantle along the N. African Plate: geochemical and isotopic evidence from the tholeiitic and alkaline volcanic rocks of the Hyblean plateau, Italy. Contributions to Mineralogy and Petrology 131, 307–322.
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Figure 2 [...] (b) 208Pb/204Pb vs. 206Pb/204Pb shown with OIB and mid-ocean ridge basalt (MORB) fields, historic Etna (Viccaro and Cristofolini, 2008) and Hyblean Plateau field from Trua et al. (1998).
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Van Orman, J.A., Grove, T.L., Shimizu, N. (2001) Rare earth element diffusion in diopside: influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates. Contributions to Mineralogy and Petrology 141, 687–703.
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As refractory elements diffusing slowly in clinopyroxene (cf. Van Orman et al., 2001), Nd and Hf may be expected to retain isotopic signatures from early crystallisation depths and exhibit large isotopic disequilibria with hosting magmas subject to mixing with recharging, or assimilating magmas, carrying isotopically distinctive compositions immediately prior to eruption.
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Vervoort, J.D., Plank, T., Prytulak, J. (2011) The Hf-Nd isotopic composition of marine sediments. Geochimica et Cosmochimica Acta 75, 5903–5926.
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Figure 2 [...] Hafnium isotopic values for Italian sediments (Conticelli et al., 2002; Brems et al., 2013) are calculated from Nd isotopic data and both cases following the seawater array (SA) and the terrestrial array (TA) of Vervoort et al. (2011) are shown.
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Viccaro, M., Cristofolini, R. (2008) Nature of mantle heterogeneity and its role in the short-term geochemical and volcanological evolution of Mt. Etna (Italy). Lithos 105, 272–288.
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Figure 2 [...] (b) 208Pb/204Pb vs. 206Pb/204Pb shown with OIB and mid-ocean ridge basalt (MORB) fields, historic Etna (Viccaro and Cristofolini, 2008) and Hyblean Plateau field from Trua et al. (1998).
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Viccaro, M., Ferlito, C., Cortesogno, L., Cristofolini, R., Gaggero, L. (2006) Magma mixing during the 2001 event at Mount Etna (Italy): effects on the eruptive dynamics. Journal of Volcanology and Geothermal Research 149, 139–159.
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Figure 1 [...] (b) Proportions of ancient Etna barometry from this study and previous work (cf. Supplementary Information, n = 287).
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Clinopyroxene from the 2001 eruption also follow the low-Y/La trend, as do other known historic and recent Etna cpx (Viccaro et al., 2006).
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Viccaro, M., Nicotra, E., Millar, I.L., Cristofolini, R. (2011) The magma source at Mount Etna volcano: Perspectives from the Hf isotope composition of historic and recent lavas. Chemical Geology 281, 343–351.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Workman, R.K., Hart, S.R., Jackson, M., Regelous, M., Farley, K.A., Blusztajn, J., Kurz, M., Staudigel, H. (2004) Recycled metasomatized lithosphere as the origin of the Enriched Mantle II (EM2) end-member: Evidence from the Samoan Volcanic Chain. Geochemistry Geophysics Geosystems 5, Q04008.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Workman, R.K., Hart, S.R. (2005) Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters 231, 53–72.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Xu, G., Frey, F.A., Clague, D.A., Abouchami, W., Blichert-Toft, J., Cousens, B., Weisler, M. (2007) Geochemical characteristics of West Molokai shield-and postshield-stage lavas: Constraints on Hawaiian plume models. Geochemistry Geophysics Geosystems 8, Q08G21.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Yamasaki, S., Kani, T., Hanan, B.B., Tagami, T. (2009) Isotopic geochemistry of Hualalai shield-stage tholeiitic basalts from submarine North Kona region, Hawaii. Journal of Volcanology and Geothermal Research 185, 223–230.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Zindler, A., Hart, S. (1986) Chemical geodynamics. Annual Review of Earth and Planetary Sciences 14, 493–571.
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Figure 2 [...] εHf vs. εNd for recent and historic Etna and the Mediterranean region. Historic Etna, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) fields from Lassiter et al., 2003; Stracke et al., 2003; Gaffney et al., 2004; Huang et al., 2005; Xu et al., 2007; Sims et al., 2008; Blichert-Toft and Albarède, 2009; Yamasaki et al., 2009; Garcia et al., 2010; Peate et al., 2010; Chekol et al., 2011; Salters et al., 2011; Viccaro et al., 2011); mantle components from Zindler and Hart, 1986; Salters and White, 1998; Workman et al., 2004; Stracke et al., 2005; Workman and Hart, 2005.
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Supplementary Information


Geologic Setting, Analytical Details, and Isotopic Measurements



Figure S-1 Location of Timpe Santa Caterina outcrop on base map from GeoMapApp (http://www.geomapapp.org; Ryan et al., 2009). Major geologic features from Rosenbaum and Lister (2004). Stratigraphy based on Corsaro et al. (2002) with section base at sea level (0 m). Dates (*) from Gillot et al. (1994).
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Timpe Santa Caterina clinopyroxene phenocrysts (typically at least 1 mm, shortest dimension) were handpicked, mounted in epoxy, and polished to 0.3 µm. Trace element concentrations were collected by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using a Nu AttoM high resolution spectrometer and New Wave UP213 (213 nm) deep-UV YAG laser ablation system at the University of New Hampshire with a ~40 μm diameter laser spot size. Samples were lightly polished to remove any sputtered debris and major element compositions near the laser pits were then analysed by electron microprobe at the University of Oregon. Major and trace element data, additional analytical details, and uncertainties are reported below (Tables S-1, S-2, and S-3). Additional cpx major element data (Table S-4) not associated with LA-ICP-MS measurements but used for thermobarometry were collected at the Massachusetts Institute of Technology (MIT).


Figure S-2 Back scattered electron images of representative clinopyroxene grains from TSC lavas with laser ablation spots (Alfred University electron microprobe).
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Table S-1 Electron microprobe analyses of TSC* clinopyroxene LA-ICP-MS laser spots. All iron reported as FeO. Operating conditions used at the University of Oregon (UO) and Massachusetts Institute of Technology (MIT) facilities were 15 keV accelerating voltage and 10 nA beam current, with all analyses using a focused beam of ~1 microns and 30 s count times. Data were reduced using the CITZAF correction procedure of Armstrong (1995). The few totals lower than 98 wt. % have been omitted. MIT JEOL JXA-8200 electron microprobe uncertainties (1σ) are calculated from the standard deviation of replicate analyses of the DJ35 diopside-jadeite glass standard and several points inferred from back scattered electron imaging to be from the same clinopyroxene crystal growth zone.
Analyses (wt. %) near laser spots TSC2_G1_3, TSC_G3_1, TSC2_G4_2, TSC7_G2_2, and TSC9_G5_2 totalled <98 wt. %. CaO abundances of the nearest same-grain spot were used to calibrate trace element concentrations (from TSC2_G1_2, TSC2_G3_2, TSC2_G4_1, TSC7_G2_1, and TSC9_G5_2, respectively).

TSC2_G1_11 σ
TSC2_G1_21 σ
TSC2_G1_41 σ
TSC2_G3_21 σ
TSC2_G3_31 σ

SiO246.190.10
46.070.10
47.400.15
49.740.10
49.770.10
TiO21.780.03
1.960.03
2.020.01
0.950.02
0.940.02
Al2O37.080.04
7.460.04
7.670.03
3.780.03
4.060.03
FeO8.700.16
9.220.16
8.990.04
8.230.15
7.850.15
MnO0.130.01
0.150.01
0.170.01
0.170.01
0.180.01
MgO12.760.05
12.530.05
11.960.05
14.710.06
14.430.06
CaO21.190.07
20.930.07
20.870.15
20.980.07
21.320.07
Na2O0.590.03
0.570.03
0.490.02
0.540.03
0.450.03
K2O0.010.01
0.000.01
0.010.01
0.010.01
0.010.01
Cr2O30.000.03
0.020.03
0.040.01
0.040.03
0.000.03
TOTAL98.43

98.91

99.62

99.14

98.99


TSC2_G3_41 σ
TSC2_G3_51 σ
TSC2_G3_61 σ
TSC2_G4_11 σ
TSC2_G2_11 σ

SiO248.410.10
48.810.10
48.210.10
48.030.10
47.130.10
TiO21.300.02
1.470.02
2.020.03
1.400.02
1.640.02
Al2O35.500.04
4.870.03
5.810.04
6.990.04
6.380.04
FeO8.650.16
7.790.15
8.330.15
7.060.14
8.620.16
MnO0.140.01
0.160.01
0.170.01
0.060.01
0.140.01
MgO13.580.06
13.800.06
13.070.05
13.400.06
13.000.05
CaO21.030.07
21.160.07
21.190.07
21.990.07
21.360.07
Na2O0.560.03
0.580.03
0.520.03
0.400.03
0.740.04
K2O0.010.01
0.000.01
0.000.01
0.010.01
0.000.01
Cr2O30.000.03
0.010.03
0.000.00
0.140.03
0.010.03
TOTAL99.18

98.65

99.31

99.49

99.02


TSC2_G2_21 σ
TSC2_G2_31 σ
TSC2_G8_11 σ
TSC2_G8_21 σ
TSC7_G2_11 σ

SiO247.510.10
48.040.10
47.340.10
47.470.10
47.370.10
TiO21.420.02
1.470.02
1.630.02
1.680.03
1.860.03
Al2O36.650.04
6.730.04
6.420.04
6.370.04
7.160.04
FeO8.230.15
8.110.15
8.620.16
8.330.15
7.830.15
MnO0.120.01
0.130.01
0.150.01
0.140.01
0.120.01
MgO13.180.06
13.200.06
12.610.05
12.470.05
12.830.05
CaO21.500.07
21.190.07
21.160.07
21.080.07
21.710.07
Na2O0.580.03
0.590.03
0.560.03
0.620.03
0.550.03
K2O0.010.01
0.000.01
0.010.01
0.000.00
0.000.01
Cr2O30.020.03
0.010.03
0.020.03
0.000.03
0.010.03
TOTAL99.22

99.47

98.51

98.15

99.43


TSC7_G5_11 σ
TSC7_G7_11 σ
TSC7_G9_11 σ
TSC7_G10_11 σ
TSC7_G10_21 σ

SiO246.860.10
48.290.10
46.400.10
48.660.10
48.800.10
TiO21.870.03
1.730.03
1.750.03
1.780.03
1.170.02
Al2O36.310.04
5.370.04
7.340.04
4.810.03
5.540.04
FeO7.830.15
7.950.15
6.650.14
7.840.15
5.690.13
MnO0.130.01
0.140.01
0.100.01
0.140.01
0.070.01
MgO12.900.05
13.290.06
13.140.05
13.240.06
14.410.06
CaO22.190.07
21.700.07
22.780.07
21.890.07
23.040.07
Na2O0.530.03
0.560.03
0.430.03
0.460.03
0.340.03
K2O0.010.01
0.000.01
0.000.01
0.000.01
0.000.01
Cr2O30.000.03
0.000.03
0.000.03
0.040.03
0.130.03
TOTAL98.63

99.04

98.59

98.85

99.18


TSC7_G10_31 σ
TSC7_G10_41 σ
TSC7_G10_51 σ
TSC7_G10_61 σ
TSC3_G1_11 σ

SiO248.240.10
49.070.10
49.500.10
49.480.10
48.680.10
TiO21.190.02
0.990.02
0.940.02
1.340.02
1.560.02
Al2O35.400.04
5.050.03
4.820.03
3.950.03
4.890.03
FeO5.550.13
5.380.12
5.420.13
7.900.15
7.470.15
MnO0.070.01
0.070.01
0.060.01
0.150.01
0.160.01
MgO14.200.06
14.540.06
14.960.06
14.110.06
13.430.06
CaO22.910.07
22.770.07
22.780.07
22.150.07
21.920.07
Na2O0.330.03
0.380.03
0.360.03
0.390.03
0.460.03
K2O0.000.01
0.000.01
0.000.01
0.000.01
0.000.01
Cr2O30.100.03
0.250.04
0.270.04
0.060.03
0.020.03
TOTAL97.99

98.50

99.12

99.52

98.59


TSC3_G1_21 σ
TSC3_G1_31 σ
TSC3_G3_11 σ
TSC3_G3_21 σ
TSC3_G3_31 σ

SiO245.120.10
46.570.10
49.080.10
48.100.10
49.310.10
TiO22.510.03
2.190.03
1.520.02
1.560.02
1.410.02
Al2O37.870.04
6.860.04
5.450.04
5.150.03
4.260.03
FeO8.340.15
8.190.15
8.530.16
7.710.15
7.610.15
MnO0.140.01
0.150.01
0.190.01
0.170.01
0.170.01
MgO11.790.05
12.350.05
13.370.06
13.580.06
14.030.06
CaO22.010.07
22.160.07
21.030.07
22.240.07
22.180.07
Na2O0.450.03
0.510.03
0.640.03
0.540.03
0.480.03
K2O0.020.01
0.000.01
0.010.01
0.000.01
0.000.01
Cr2O30.000.03
0.010.03
0.020.03
0.010.03
0.000.03
TOTAL98.26

98.99

99.85

99.05

99.47


TSC3_G9_11 σ
TSC3_G9_31 σ
TSC3_G9_41 σ
TSC9_G1_11 σ
TSC9_G1_21 σ

SiO249.350.10
49.340.10
47.900.10
48.320.10
47.920.10
TiO21.590.02
1.320.02
1.950.03
1.250.02
1.690.03
Al2O35.200.04
4.430.03
6.230.04
6.290.04
5.820.04
FeO8.360.15
7.610.15
8.180.15
8.430.15
7.210.14
MnO0.160.01
0.150.01
0.150.01
0.140.01
0.110.01
MgO13.430.06
14.100.06
12.900.05
13.000.05
13.250.06
CaO22.260.07
22.560.07
21.800.07
22.060.07
22.000.07
Na2O0.570.03
0.370.03
0.480.03
0.430.03
0.440.03
K2O0.000.01
0.000.01
0.010.01
0.010.01
0.010.01
Cr2O30.050.03
0.000.03
0.020.03
0.000.03
0.000.03
TOTAL100.96

99.87

99.62

99.93

98.45


TSC9_G3_11 σ
TSC9_G3_21 σ
TSC9_G5_11 σ






SiO247.390.10
48.740.10
47.550.10





TiO21.970.03
1.630.02
1.630.03





Al2O35.610.04
5.290.04
4.870.03





FeO7.520.15
7.270.14
7.660.15





MnO0.140.01
0.130.01
0.170.01





MgO13.190.06
13.600.06
13.440.06





CaO22.330.07
22.160.07
22.480.07





Na2O0.560.03
0.530.03
0.460.03





K2O0.020.01
0.020.01
0.010.01





Cr2O30.010.03
0.000.03
0.040.03





TOTAL98.74

99.36

98.31






* TSC samples were collected from a cliff below Via Pianetto at 37°36’21” N and 15°10’20” E from the base at sea level to the top, approximately 85 m above, as shown in the cross section of Figure S-1.

Download in Excel

Table S-2 Trace element data (ppm) collected by LA-ICP-MS at the University of New Hampshire.

TSC2_G1_11 s.e.
TSC2_G1_21 s.e.
TSC2_G1_31 s.e.
TSC2_G1_41 s.e.
TSC2_G3_11 s.e.

Li507
10314
558
608
547
Sc1053
913
973
973
983
Ti10307233
8896154
9244187
10272294
591198
V31713
25711
31814
32715
22410
Cr663
592
603
513
242
Ni687
586
626
383
514
Sr1327
1246
1166
1288
1327
Y541
451
421
462
381
Zr1284
1074
994
1146
753
Nb0.90.3
1.60.2
0.890.2
1.00.2
0.60.1
Sn2.30.3
1.00.3
1.80.2
4.20.3
1.60.4
La151
12.00.9
11.20.7
141
11.00.8
Ce484
423
373
484
393
Pr9.30.9
7.90.8
7.20.7
91
7.10.7
Nd494
433
383
453
383
Sm14.00.7
121
11.00.5
12.20.7
9.60.4
Eu4.50.5
4.00.4
3.30.3
4.60.4
3.50.3
Gd152
151
121
132
10.00.8
Tb2.30.2
2.20.2
1.50.1
1.80.2
1.80.1
Dy14.00.5
101
9.70.6
121
10.40.5
Ho2.50.1
2.250.2
2.00.1
1.90.1
1.90.1
Er7.70.7
5.10.6
5.00.5
5.40.7
4.40.6
Tm0.880.07
0.620.09
0.720.02
0.50.1
0.600.02
Yb3.60.4
3.90.3
3.90.3
3.20.5
2.60.3
Lu0.490.07
0.60.1
0.450.09
0.50.2
0.40.1
Hf8.20.8
7.40.5
5.00.6
81
4.70.5
Pb0.140.03
0.170.03
0.190.03
0.40.3
0.210.05
Th0.290.03
0.200.03
0.190.03
0.250.03
0.130.02
U0.0250.009
0.0290.008
0.0380.010
0.0020.009
0.0080.008


TSC2_G3_21 s.e.
TSC2_G3_31 s.e.
TSC2_G3_41 s.e.
TSC2_G3_51 s.e.
TSC2_G3_61 s.e.

Li142
5.40.7
142
91
162
Sc1133
1063
968
902
893
Ti488885
4772102
5551390
6382173
6255125
V2189
23410
24919
27314
26911
Cr241
301
323
462
422
Ni413
374
383
423
393
Sr844
774
746
824
864
Y21.60.6
20.20.6
182
20.40.7
200.6
Zr472
402
382
442
442
Nb0.360.06
0.410.08
0.290.08
0.590.09
0.80.1
Sn0.50.1
0.50.2
0.70.2
0.70.2
0.70.1
La5.10.4
4.30.3
4.20.4
4.60.3
5.10.3
Ce181
161
142
181
181
Pr3.60.4
3.30.3
30.4
3.30.3
3.70.4
Nd212
162
161
161
201
Sm5.10.3
4.30.2
4.20.7
3.90.1
3.80.2
Eu1.40.2
1.40.1
1.20.1
1.20.1
1.40.2
Gd6.70.8
4.80.4
40.8
4.90.4
5.80.5
Tb1.10.1
0.90.1
10.1
0.960.06
10.1
Dy4.90.2
4.40.2
3.40.6
3.90.3
4.70.4
Ho0.740.06
0.690.07
0.630.02
0.750.05
0.590.03
Er2.30.3
1.90.2
1.60.4
1.60.2
1.90.2
Tm0.290.05
0.280.02
0.280.06
0.340.05
0.330.04
Yb1.80.1
1.40.2
1.80.2
1.10.2
10.2
Lu0.220.05
0.230.04
0.190.03
0.190.03
0.220.03
Hf1.60.2
1.40.1
1.40.2
1.40.2
1.40.2
Pb0.0680.008
0.130.03
0.080.02
0.130.02
0.140.04
Th0.0500.008
0.0450.006
0.050.01
0.050.01
0.110.01
U0.0070.003
0.0070.002
0.0130.002
0.0090.002
0.0160.002


TSC2_G4_11 s.e.
TSC2_G4_21 s.e.
TSC2_G2_11 s.e.
TSC2_G2_21 s.e.
TSC2_G2_31 s.e.

Li537
598
183
466
284
Sc1314
1295
1173
1053
1396
Ti6293115
6055128
8882153
6910140
8867314
V27511
27912
31414
28812
33217
Cr64223
64027
423
543
443
Ni1067
1077
524
684
393
Sr995
844
1126
955
895
Y181
170.6
411
362
382
Zr342
301
843
1027
814
Nb0.420.08
0.10.1
0.60.1
4.70.5
1.10.2
Sn0.50.2
0.50.2
1.60.2
0.80.2
1.20.3
La4.10.3
3.20.2
11.40.7
222
10.10.8
Ce131
10.90.9
353
535
313
Pr2.50.3
2.20.3
6.60.7
81
60.6
Nd131
121
383
374
322
Sm3.60.5
3.10.2
10.40.9
8.80.8
9.50.2
Eu1.50.2
10.1
3.10.3
2.40.3
2.70.3
Gd50.7
5.30.8
131
101
101
Tb0.70.1
0.560.09
1.60.1
1.40.1
1.30.1
Dy3.30.1
40.4
8.20.6
7.90.3
7.50.4
Ho10.04
0.610.03
1.50.1
1.40.1
1.40.1
Er1.10.3
1.70.3
4.80.4
4.30.5
3.30.4
Tm0.270.07
0.230.07
0.550.06
0.60.1
0.340.04
Yb1.30.2
0.60.3
3.50.2
3.10.3
2.40.4
Lu0.320.04
0.210.09
0.540.09
0.70.1
0.350.06
Hf1.10.2
1.30.1
4.20.4
3.30.5
3.40.3
Pb0.030.02
0.090.03
0.080.02
1.40.19
0.110.04
Th0.0620.005
0.040.01
0.20.01
1.80.2
0.190.02
U0.0070.002
0.0060.003
0.0180.004
0.190.03
0.0240.004


TSC2_G8_11 s.e.
TSC2_G8_21 s.e.
TSC7_G2_11 s.e.
TSC7_G2_21 s.e.
TSC7_G5_11 s.e.

Li101
345
213
5.80.8
2.70.4
Sc1013
1074
1073
1003
1275
Ti8210151
8450374
10814216
9617196
9624290
V30213
30618
31414
32113
26512
Cr522
482
766
683
36039
Ni464
443
574
463
566
Sr855
765
1387
1156
1137
Y271
252
361
372
281
Zr623
623
943
953
795
Nb0.40.1
0.70.1
1.40.2
0.60.1
0.70.2
Sn0.80.2
0.60.2
1.60.3
1.20.1
2.70.6
La6.90.4
6.50.5
9.20.7
9.10.6
6.30.7
Ce245
212
312
353
242
Pr4.50.5
4.50.5
60.6
6.80.7
4.60.5
Nd212
212
323
363
282
Sm7.30.5
6.10.4
9.20.9
9.20.6
6.30.3
Eu2.10.2
1.60.2
30.5
3.60.4
2.70.3
Gd6.90.9
5.90.7
10.70.8
8.40.7
6.40.8
Tb10.1
0.910.06
1.60.1
1.50.1
1.230.09
Dy5.90.5
5.60.2
6.50.4
7.20.4
6.20.3
Ho0.830.08
0.830.08
1.70.2
1.70.1
1.20.1
Er3.30.6
3.60.5
4.40.8
3.40.4
2.60.5
Tm0.240.03
0.240.03
0.460.09
0.510.03
0.270.08
Yb20.2
1.90.2
2.80.2
2.50.3
1.50.3
Lu0.270.08
0.240.05
0.40.1
0.320.05
0.290.06
Hf2.70.2
3.10.3
3.40.4
3.90.3
3.90.4
Pb0.080.02
0.050.02
0.120.05
0.130.02
0.10.03
Th0.120.02
0.090.01
0.150.03
0.150.02
0.0790.008
U0.0180.006
0.0170.006
0.0190.006
0.0160.006
0.0070.003


TSC7_G7_11 s.e.
TSC7_G9_11 s.e.
TSC7_G10_11 s.e.
TSC7_G10_21 s.e.
TSC7_G10_31 s.e.

Li5.10.7
3.80.6
6.90.9
4.30.6
5.40.8
Sc1455
1254
1333
1343
1434
Ti11294172
9592192
8341236
6522169
6252113
V34314
29813
32515
24011
23910
Cr442
1094
75138
100546
82439
Ni494
886
506
905
875
Sr1367
1378
804
683
684
Y471
231
231
100
100
Zr1375
563
733
241
231
Nb1.50.1
0.530.09
0.70.1
0.090.07
0.130.04
Sn2.10.4
2.40.4
0.50.2
0.60.2
0.540.07
La151
5.50.4
6.20.5
1.80.2
1.60.1
Ce484
202
232
70.6
6.80.5
Pr9.10.9
3.90.4
4.30.4
1.50.2
1.40.1
Nd484
232
232
7.80.8
8.10.6
Sm12.50.4
5.60.4
5.60.6
2.60.3
2.70.3
Eu4.30.4
20.3
1.60.1
0.810.09
0.80.07
Gd11.50.9
5.90.8
6.80.6
2.50.3
2.40.3
Tb1.90.2
1.110.09
10.1
0.510.05
0.480.07
Dy10.20.7
4.90.6
4.10.2
2.50.3
1.880.06
Ho2.60.3
1.20.1
0.80.03
0.310.02
0.350.03
Er4.30.5
2.70.3
2.50.3
0.810.09
0.90.1
Tm0.760.06
0.180.04
0.250.04
0.120.03
0.120.01
Yb3.30.5
1.40.1
1.90.3
0.70.2
0.90.1
Lu0.490.14
0.330.06
0.330.04
0.050.04
0.130.04
Hf5.90.6
2.50.3
3.90.3
1.60.2
1.50.1
Pb0.160.03
0.060.01
0.080.02
0.0250.003
0.050.02
Th0.250.03
0.080.02
0.080.01
0.020.01
0.030.008
U0.0210.003
0.0170.006
0.0110.004
nd

0.0040.003


TSC7_G10_41 s.e.
TSC7_G10_51 s.e.
TSC7_G10_61 s.e.
TSC3_G1_11 s.e.
TSC3_G1_21 s.e.

Li3.30.5
2.40.4
30.4
2.60.6
1.30.3
Sc1314
1315
1445
812
913
Ti5276143
5415101
7483175
7430159
10948178
V21012
2219
28212
1738
2189
Cr2332116
136359
693
191
151
Ni935
895
362
244
262
Sr643
623
764
18810
19610
Y91
90
191
361
401
Zr191
201
522
1354
1935
Nb0.180.02
0.150.05
0.340.03
10.1
2.10.2
Sn0.420.05
0.360.06
0.80.1
1.70.3
2.20.4
La1.60.1
1.470.09
4.40.3
171
241
Ce6.20.5
5.60.5
161
504
675
Pr1.30.2
1.20.1
3.20.3
111
141
Nd7.20.6
7.10.7
191
575
725
Sm2.40.6
2.40.2
4.40.3
10.60.5
140.7
Eu0.770.06
0.70.1
1.50.2
4.20.4
5.10.6
Gd1.90.2
2.80.2
5.50.6
161
182
Tb0.240.03
0.460.03
0.710.07
1.90.2
1.80.2
Dy1.70.1
1.810.3
4.20.1
9.80.4
100.6
Ho0.290.04
0.290.03
0.760.04
1.70.2
1.720.08
Er10.1
0.70.1
2.30.2
2.90.3
3.70.5
Tm0.090.02
0.10.04
0.180.03
0.530.05
0.60.1
Yb0.490.08
0.50.03
1.80.3
3.10.4
2.20.6
Lu0.080.01
0.070.02
0.190.05
0.40.06
0.50.1
Hf0.90.1
1.30.2
2.30.3
5.40.4
7.40.6
Pb0.030.01
0.030.01
0.040.01
0.110.02
0.080.01
Th0.0150.004
0.0270.006
0.0530.006
0.210.01
0.420.06
U0.0030.002
0.0030.001
0.0080.001
0.0210.005
0.0450.006


TSC3_G1_31 s.e.
TSC3_G3_11 s.e.
TSC3_G3_21 s.e.
TSC3_G3_31 s.e.
TSC3_G9_11 s.e.

Li3.40.6
4.50.7
10.3
0.90.2
6.61
Sc933
602
843
1013
1134
Ti10122201
7869133
7534145
6712123
8850302
V21318
1958
1868
1949
26812
Cr9.50.8
11.60.5
10.30.8
101
11.50.7
Ni213
212
171
142
183
Sr25519
1638
1578
1498
18112
Y401
31.70.8
29.60.7
291
37.90.9
Zr1866
1144
1093
1144
1836
Nb5.40.8
1.10.1
0.760.07
0.90.1
1.80.1
Sn1.70.4
0.90.2
0.70.3
0.60.2
0.80.2
La262
15.50.9
14.20.9
13.50.8
191
Ce686
453
423
403
646
Pr131
91
91
8.30.8
121
Nd665
484
433
383
534
Sm13.70.7
111
101
9.70.6
12.80.6
Eu3.90.3
40
30
3.10.3
3.40.3
Gd172
121
121
9.90.8
131
Tb1.60.2
1.60.2
1.40.2
1.30.1
1.80.1
Dy9.60.7
7.40.4
6.10.3
5.50.4
90.5
Ho1.40.05
1.480.08
1.070.07
1.10.08
1.40.1
Er3.10.5
2.90.4
2.70.4
3.20.4
4.30.6
Tm0.540.05
0.390.08
0.290.04
0.40.06
0.380.07
Yb2.50.5
2.80.5
2.20.3
2.80.6
2.30.1
Lu0.290.07
0.340.07
0.380.08
0.310.08
0.40.06
Hf7.30.7
4.20.3
4.40.4
4.30.3
6.80.7
Pb0.90.2
0.070.01
0.110.01
0.040.01
0.160.03
Th1.20.2
0.230.03
0.150.01
0.170.02
0.350.04
U0.320.06
0.0210.004
0.0110.003
0.0230.003
0.0620.008


TSC3_G9_31 s.e.
TSC3_G9_41 s.e.
TSC9_G1_11 s.e.
TSC9_G1_21 s.e.
TSC9_G3_11 s.e.

Li0.30.3
1.30.2
365
335
284
Sc1054
882
531
782
1143
Ti9521375
9280198
587595
8005159
10648166
V27814
24210
22710
26313
2169
Cr212
13.90.7
363
422
231
Ni322
233
372
354
222
Sr1548
1689
1238
1167
1507
Y25.80.8
30.80.9
15.60.4
21.40.8
31.10.9
Zr1084
1304
491
672
1424
Nb1.40.2
1.20.2
0.50.1
0.610.07
1.10.1
Sn1.10.2
0.80.2
0.530.06
10.2
1.60.2
La12.20.8
14.80.9
60.4
80.5
14.50.9
Ce413
504
242
313
484
Pr8.10.8
101
4.20.4
5.60.6
8.70.9
Nd363
443
212
282
463
Sm9.20.4
111
5.80.5
7.60.5
11.60.4
Eu2.90.2
3.40.3
1.70.2
2.60.4
3.20.3
Gd8.70.9
9.80.8
4.60.5
6.70.9
10.70.9
Tb1.170.08
1.30.1
0.680.09
0.910.06
1.30.1
Dy50.1
6.60.3
3.70.5
5.60.4
7.40.4
Ho0.990.06
1.10.1
0.830.02
1.130.09
1.60.1
Er3.30.3
2.80.5
1.70.3
2.30.2
3.60.4
Tm0.390.06
0.420.03
0.210.02
0.240.03
0.280.02
Yb1.80.3
2.50.2
1.20.2
1.250.05
20.4
Lu0.290.08
0.370.05
0.070.02
0.180.02
0.290.04
Hf3.70.2
4.40.4
2.20.2
30.2
6.30.4
Pb0.040.01
0.050.01
0.040.02
0.040.02
0.10.01
Th0.190.01
0.190.02
0.0880.006
0.10.02
0.20.01
U0.0170.007
0.0210.005
0.0170.004
0.0190.005
0.0250.003


TSC9_G3_21 s.e.
TSC9_G5_11 s.e.
TSC9_G5_21 s.e.






Li243
183
101





Sc992
995
1143





Ti8647135
9205538
10315165





V1848
25514
27112





Cr211
243
71





Ni262
274
182





Sr1467
15114
1849





Y24.50.9
241
401





Zr943
987
1586





Nb0.820.07
0.80.1
1.80.2





Sn1.20.2
1.10.2
1.40.4





La10.30.6
141
241





Ce353
535
877





Pr6.30.6
80.8
141





Nd353
393
645





Sm9.20.4
91
161





Eu2.30.2
2.60.2
50





Gd8.40.9
81
151





Tb10.1
1.040.07
20





Dy6.10.3
5.50.4
10.30.5





Ho0.90.1
0.990.08
1.50.07





Er2.40.3
2.50.4
3.70.3





Tm0.30.05
0.290.06
0.390.04





Yb1.30.2
1.70.2
3.20.2





Lu0.260.04
0.160.03
0.440.06





Hf3.80.2
4.50.5
6.80.4





Pb0.050.01
0.220.05
0.140.03





Th0.1170.008
0.180.03
0.230.02





U0.0340.005
0.0330.008
0.040.005





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Trace element analytical methods
Trace element concentrations of TSC clinopyroxenes were collected by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using a Nu AttoM high resolution spectrometer and New Wave UP213 (213 nm) deep-UV YAG laser ablation system at the University of New Hampshire. Laser spots on sample material were ~40 μm in diameter.

The concentration of trace element i in the clinopyroxene sample, (Cisample), reported in ppm, was calculated using the following relationship:

Eq. S-1 


Calcium concentrations (CCasample), measured near each laser ablation pit by electron microprobe, served as the internal reference element. I represents the background corrected signal intensity of a material and R denotes the reference standard glass, ML3B-G. Trace element signal intensities were calculated from LA-ICP-MS measurements via the following processing procedure: an ablation interval of typically 12–15 peak count cycles was corrected for background by subtracting a background count average (typically of 24 background cycles, with half taken before sample count collection and half after) from each cycle collected within the ablation interval (the sample peak). The median of either four or five sub-intervals within the ablation interval was used to represent the background corrected sample count value (Iisample). ML3B-G glass served as the reference standard and two ML3B-G points were measured between every set of five unknowns. Background corrected count values for the ML3B-G glass standard (IiR) were collected in the same manner. Concentrations at each sample location were calculated using the reference standard signals collected closest in time to the sample measurement over the course of the analyses.

The error propagated for each analysis consisted of the standard error (s.e.) of the mean for the subintervals of sample peak selected, the uncertainty of internal standard electron microprobe Ca measurement, and the uncertainty of the calibration standard ML3B-G measurements, which was taken as the difference between the reported ML3B-G concentrations (Jochum et al., 2006) and the average of repeat analyses of ML3B-G over the course of the TSC clinopyroxene measurements reported in this study.

Table S-3 Comparison of LA-ICP-MS repeat analyses of ML3B-G glass standard with reported literature values.

ML3B-G*LA-ICP-MS




literature valueaverage




ppmppmΔ lit-avg Δ as %1 σ* 1 σ as %
Li4.505.200.7015.50.9321
Sc31.6031.01-0.59-1.91.304
Ti12769.7812823.9554.160.4368.343
V268.00278.6410.644.017.927
Cr177.00182.945.943.49.816
Ni107.00112.635.635.36.766
Sr312.00327.3215.324.921.967
Y23.9024.290.391.61.858
Zr122.00124.982.982.48.767
Nb8.619.170.566.50.9311
Sn1.141.160.021.40.3833
La8.999.530.546.00.9711
Ce23.1024.951.858.02.6912
Pr3.433.800.3710.70.4914
Nd16.7017.951.257.52.2213
Sm4.754.790.040.80.7315
Eu1.671.810.148.60.2112
Gd5.265.670.417.80.9217
Tb0.800.840.045.50.1823
Dy4.844.850.010.20.5812
Ho0.910.910.000.50.1314
Er2.442.640.208.40.4117
Tm0.320.330.001.50.0620
Yb2.062.00-0.06-2.70.4522
Lu0.290.320.0413.20.0828
Hf3.223.420.206.20.7624
Pb1.381.530.1510.50.2317
Th0.550.570.024.50.0611
U0.440.500.0512.20.0920

* ML3B-G was analysed twice between every 5 unknown samples, totalling 24 standard analyses during collection of the TSC data reported in this study. Analytical uncertainty is determined by having the first of each two ML3B-G analyses serve as the 'standard' for calculating the concentration of the second ML3B-G analysis, which is run as an unknown sample. The average value of the 12 ML3B-G 'unknowns' is compared here with the literature values for these trace elements (Jochum et al., 2006) along with the standard deviation of these ML3B-G runs.

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Table S-4 TSC clinopyroxene major element compositions (wt. %) along grain transects were analysed on the Massachusetts Institute of Technology (MIT) JEOL-JXA-8200 Superprobe. Uncertainty (2s) has been calculated from the standard deviation of replicate analyses of the DJ35 diopside-jadeite glass and ALP7 aluminous orthopyroxene standards, as well as several points inferred from back scattered electron imaging to be from the same clinopyroxene crystal growth zone: SiO2 (0.31), TiO2 (0.02), Al2O3 (0.07), FeO (0.08), MgO (0.11), MnO (0.01), CaO (0.30), Na2O (0.04), K (0.01), Cr2O3 (0.02).

SiO2TiO2Al2O3FeOtMnOMgOCaONa2OK2OCr2O3Total
TSC-2A-247.741.416.87.170.1113.0921.80.30.010.0198.44
TSC-2A-348.571.36.497.950.1312.8221.420.400.0499.12
TSC-2A-447.881.296.47.710.1313.2221.280.3600.0498.31
TSC-2A-548.711.236.177.940.1513.4421.440.4400.0399.54
TSC-2A-649.171.125.337.710.1413.8521.370.4600.0399.18
TSC-2A-748.691.245.596.350.0914.2322.090.420.010.0498.74
TSC-2A-849.571.185.646.440.114.2522.380.3200.0399.9
TSC-2A-949.471.145.596.650.114.1722.140.4200.0199.69
TSC-2A-1048.871.196.587.250.0913.5422.20.480.020.04100.26
TSC-2A-1148.631.26.497.260.1213.7521.790.4400.0599.71
TSC-2A-1248.941.226.337.150.1113.7721.930.40.010.0399.89
TSC-2A-1349.21.035.967.030.1413.9521.880.350.010.0799.62
TSC-2B-249.451.283.848.310.1914.5620.990.5400.0599.21
TSC-2B-348.121.514.987.970.1414.2720.910.550.010.0198.47
TSC-2B-449.780.994.177.770.1614.9321.220.500.0199.53
TSC-2B-550.210.923.647.770.1715.1720.930.4800.0199.31
TSC-2B-650.430.923.787.790.1815.2421.380.4300100.16
TSC-2B-750.431.133.867.80.1714.8921.340.3700.01100
TSC-2B-850.830.933.547.930.1814.9920.850.4100.0199.67
TSC-2B-950.960.993.697.940.1814.9521.130.3800100.21
TSC-2B-1050.380.993.767.850.1915.2221.330.4700.002100.18
TSC-2C-147.42.027.678.990.1711.9620.870.490.010.0499.62
TSC-2C-246.541.937.238.730.1712.420.590.530.010.0698.19
TSC-2C-346.511.967.238.690.1512.7420.780.4800.0498.59
TSC-2C-446.471.947.2690.1813.120.740.5800.0199.29
TSC-2C-546.711.877.038.840.1812.9920.790.5800.0299.01
TSC-2C-646.931.847.028.760.1513.0920.810.580.010.0299.21
TSC-2C-747.071.836.918.670.1713.2120.950.5300.0399.37
TSC-2C-846.791.877.138.990.1713.2420.880.5200.0199.6
TSC-2C-946.531.896.988.910.1713.3721.20.5600.0299.63
TSC-2C-1049.140.883.977.750.1715.5821.380.580.01099.45
TSC-2D-248.91.423.937.770.1613.9321.670.3500.0498.17
TSC-2D-349.11.43.857.720.1414.2321.630.410.010.0498.53
TSC-2D-450.421.243.517.620.1314.5521.870.4300.0399.79
TSC-2D-549.851.384.017.960.1414.3321.960.400.04100.06
TSC-2D-650.451.324.017.450.1514.2821.730.530.010.0299.95
TSC-2D-750.011.23.57.90.1614.8121.750.470.010.0199.82
TSC-2D-849.811.423.847.60.1714.6822.120.4500.02100.13
TSC-2D-949.321.584.198.110.1614.3521.760.400.0399.9
TSC-2D-1046.771.554.538.30.1714.7921.510.5200.0198.15
TSC-3A-149.141.614.817.46013.7122.470.510099.72
TSC-3A-249.091.674.737.42013.6122.520.460099.5
TSC-3A-349.011.654.998.19013.3121.660.610099.43
TSC-3A-4482.195.638.61012.6722.030.610099.74
TSC-3A-548.682.024.918.23012.9622.160.680099.64
TSC-3A-649.222.044.139.22012.6722.130.660.010100.09
TSC-3A-747.92.315.098.670.0212.5622.050.630099.23
TSC-3A-850.421.512.969.240.0212.8322.010.70099.69
TSC-3A-945.82.747.38.890.0212.121.90.540099.29
TSC-3A-1049.911.394.117.920.0113.9621.640.570099.51
TSC-3A-1149.491.474.727.330.0113.8922.090.550099.55
TSC-3A-1249.741.464.618.23013.7121.490.570099.81
TSC-3B-150.230.954.595.24014.9723.050.3900.1899.6
TSC-3B-250.090.964.775.4014.9222.930.4300.1799.67
TSC-3B-349.471.145.285.47014.8822.820.4600.2199.73
TSC-3B-449.351.15.435.64014.6222.720.4300.1599.44
TSC-3B-550.120.894.795.38014.9822.80.400.1999.55
TSC-3B-649.281.145.45.56014.4622.840.4100.1199.21
TSC-3B-749.331.125.265.40.0214.4922.850.470.010.2499.18
TSC-3B-849.291.015.025.340.0214.6822.640.500.2298.72
TSC-3B-949.11.564.387.87013.9122.150.470099.45
TSC-3B-1049.881.523.867.930.0114.0822.050.410099.74
TSC-3B-1149.511.175.45.54014.6322.980.3800.1799.77
TSC-3B-1249.411.115.335.48014.4922.830.4200.1899.26
TSC-3C-148.5524.968.44013.0622.20.5400.0299.76
TSC-3C-248.062.155.268.53012.9122.20.560099.67
TSC-3C-348.1924.968.52012.9722.380.5900.0599.66
TSC-3C-4482.125.148.52012.6821.960.620099.04
TSC-3C-548.282.024.938.33012.7522.130.6400.0299.09
TSC-3C-647.432.465.488.89012.4321.930.620099.24
TSC-3C-749.681.663.698.22013.4621.620.610098.95
TSC-3C-848.781.884.658.46012.9822.010.580.010.0499.38
TSC-3C-947.951.895.448.35013.2322.190.4600.0199.52
TSC-3C-1048.322.084.948.66012.8921.850.6400.0299.4
TSC-3C-1147.712.365.488.73012.5722.070.580099.5
TSC-3D-147.722.055.728.19012.8222.30.560099.36
TSC-3D-247.942.135.518.46012.9722.130.540.01099.69
TSC-3D-348.271.85.258.24012.9722.260.580.01099.38
TSC-3D-448.211.995.277.860.0313.0622.310.5200.0199.26
TSC-3D-547.372.276.038.16012.6322.380.560.01099.4
TSC-3D-647.612.185.828.37012.5522.140.650099.32
TSC-3D-748.352.164.888.61012.9921.720.670099.38
TSC-3D-848.831.645.048.160.0313.222.070.630.01099.61
TSC-3D-948.051.476.257.53013.5122.240.510099.56
TSC-3D-1048.651.395.937.52013.7222.170.5200.0199.92
TSC-7A-147.741.595.467.830.1814.0421.510.770099.13
TSC-7A-248.721.44.857.680.1814.1221.690.6400.0299.3
TSC-7A-348.551.484.777.70.1714.0921.710.4700.0498.97
TSC-7A-449.071.44.377.70.1614.221.730.560.010.0399.23
TSC-7A-549.591.33.937.50.1614.2621.910.5800.0599.28
TSC-7A-648.731.594.547.640.1513.7322.170.480.020.0399.09
TSC-7A-749.011.54.377.730.1713.6822.060.5100.0299.04
TSC-7A-849.311.384.367.520.1613.9321.930.4700.0299.08
TSC-7A-949.921.374.247.50.1513.9621.860.5100.0499.55
TSC-7A-1050.131.324.277.460.1613.6321.720.4100.0299.13
TSC-7B-249.941.263.987.380.1714.2321.940.470.01099.38
TSC-7B-348.581.464.777.280.1813.9521.970.380.01098.59
TSC-7B-449.141.294.487.490.1514.2721.660.4900.0398.99
TSC-7B-548.321.284.087.230.1614.8721.80.3700.0298.12
TSC-7B-650.091.263.767.520.1614.0321.560.460.010.0198.86
TSC-7B-749.821.223.747.580.1914.1621.450.4700.0298.65
TSC-7B-846.932.045.917.770.1413.1121.940.4600.0598.35
TSC-7B-947.132.095.688.230.1512.8721.810.4900.0198.46
TSC-7B-1047.351.875.817.750.1513.4921.870.60.01098.9
TSC-9A-147.952.585.029.03012.4722.060.700.0199.82
TSC-9A-248.041.985.817.42013.2322.820.520099.82
TSC-9A-348.182.225.458.290.0513.0722.440.7200.03100.44
TSC-9A-447.852.095.627.890.0313.0222.30.580099.38
TSC-9A-547.062.376.668.020.0312.8222.890.5100100.37
TSC-9A-647.762.335.938.060.0112.8222.290.6200.0599.86
TSC-9A-748.561.75.277.490.0213.5422.810.560099.95
TSC-9A-849.441.684.517.070.0114.0222.460.4800.0199.67
TSC-9A-949.621.674.077.60.0213.621.950.680099.21
TSC-9A-1047.122.066.598.45012.722.080.520099.52
TSC-9B-147.852.135.797.71013.0522.350.5600.0299.47
TSC-9B-249.761.334.177.540.0114.0321.870.6200.0199.34
TSC-9B-348.411.735.127.630.0313.3822.20.510.01099.02
TSC-9B-449.421.434.357.070.0314.1822.460.530.010.0199.49
TSC-9B-549.631.514.497.380.0213.8921.810.620.01099.36
TSC-9B-650.171.423.737.240.0214.1622.260.50099.5
TSC-9B-749.731.54.247.510.0213.822.10.590099.48
TSC-9B-849.371.674.447.61013.9222.380.6200.04100.05
TSC-9B-949.631.464.397.06014.1722.660.460099.83
TSC-9B-1050.251.33.717.21014.5822.580.4400.01100.09
TSC-9C-146.862.556.228.380.0212.7122.490.590099.82
TSC-9C-248.481.885.027.650.0313.3222.520.590099.49
TSC-9C-350.561.553.267.690.0114.321.370.620.01099.37
TSC-9C-449.81.423.977.39014.1221.850.490.01099.04
TSC-9C-549.991.413.887.15014.2921.910.520099.15
TSC-9C-649.341.674.397.5013.8421.670.580.01098.99
TSC-9C-749.241.634.317.560.0113.721.990.530098.96
TSC-9C-848.811.785.017.59013.4822.480.640.01099.8
TSC-9C-948.871.635.167.15013.6622.70.530.01099.71
TSC-9C-1046.412.546.998.16012.5122.640.560.01099.82

*Operating conditions of the MIT JXA-8200 consisted of a 15 keV accelerating voltage and 10 nA beam current, with all analyses using a focused beam of ~1 μm and 30 s count times. Data were reduced using the CITZAF correction procedure of Armstrong (1995). The few totals lower than 98 wt. % have been omitted.
† All iron reported as FeO

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Neodymium, Hf, and Pb isotopic compositions were measured on the Nu Plasma 500 HR multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) at the Ecole Normale Supérieure de Lyon.

Table S-5 Hf-Nd-Pb isotopic data for Timpe Santa Caterina whole rock (WR) and clinopyroxene (cpx) separates*. The uncertainties reported for Nd and Hf isotope ratios are internal 2 s.e. We use the values of external reproducibility as reported in the footnote to identify analytically resolvable WR-cpx disequilibrium discernable above the 2σ level.

143Nd/144NdεNd176Hf/177Hf †εHf §206Pb/204Pb §207Pb/204Pb §208Pb/204Pb #
TSC-2
     WR0.512952(2)6.10.283035(5)9.320.01515.66839.645
     cpx0.512942(3)5.90.283033(4)9.220.01415.67039.645

TSC-3
     WR0.512948(3)60.283032(4)9.220.07815.67039.666
     cpx0.512937(2)5.80.283047(6)9.720.07215.66839.655

TSC-7
     WR0.512929(4)5.70.283012(4)8.519.99015.67639.648
     cpx0.512921(2)5.50.283024(6)8.919.94615.66839.587

TSC-9
     WR0.512930(3)5.70.283014(4)8.619.98715.67539.647
     cpx0.512922(3)5.50.282996(4)7.919.97815.66939.620

* WR samples (italicised) are from Bryce et al. (2011) and are reported here for convenience. For the clinopyroxene samples, aliquots of 0.5 to 2 mm clinopyroxene handpicked from the TSC lavas were first leached in hot (~120° C) 6 N HCl to remove any Pb surface contamination following techniques outlined in Blichert-Toft and Albarède (2009). The resulting residues were subsequently digested in a mixture of concentrated HF-HNO3. Lead was separated prior to Hf and Nd separation using techniques described in Bryce and DePaolo (2004). Total Pb procedural blanks were <40 pg. Hafnium was separated from the Pb column eluent using the three column procedure described for high magnesium samples by Blichert-Toft (2001). Neodymium was from the Pb column eluent, separated from the residue of the first Hf column using a three column procedure starting with a small (0.5 mL) cation exchange resin (AG50x8) to strip off Fe and other major ions. The REE-rich elutions were subsequently passed through a 0.5 mL column filled with TRU-Spec resin to concentrate further the REEs, where the 2 M HNO3 was used to elute other ions and the REEs were collected with water. Nd was finally separated from Sm using a 1.6 mL LN-Spec column and a 0.25 M HCl elution. Total Nd procedural blanks were <30 pg and total Hf procedural blanks were <20 pg.

† For the Nd isotopic measurements, instrument performance was monitored with a laboratory solution, and accuracy was assessed through repeated (n = 9) analyses of BCR-1 which yielded 0.512638 (with external 2σ = 0.000020). εNd was calculated using a CHUR value of 143Nd/144Nd = 0.512638.

§ Hf isotopic analyses were obtained following the techniques described in Blichert-Toft et al. (1997). The 100 ppb JMC 475 Hf standard, run throughout the analytical session (n = 21) to monitor instrument performance, yielded 176Hf/177Hf = 0.282160 (with external 2σ = 0.000015). εHf was calculated using a CHUR value of 176Hf/177Hf = 0.282772 (Blichert-Toft and Albarède, 1997).

# Mass fractionation in Pb isotope analyses was corrected via Tl normalisation as described in White et al. (2000), and ratios were additionally adjusted for drift using the standard bracketing technique outlined in Albarède et al. (2004) using the NIST SRM values reported in Eisele et al. (2003). Four NIST SRM 981 samples, run as “blind” amongst the 17 bracketing standards analysed, yielded averages (with 2σ external precision) of 208Pb/204Pb = 36.7271 (0.0019), 207Pb/204Pb = 15.4978 (0.0009) and 206Pb/204Pb = 16.9408 (0.0012).

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Clinopyroxene Thermobarometry Model Evaluation


Experimental dataset
Although cpx-liquid thermobarometry (Putirka et al., 2003) has been used successfully with recent Etna lavas (e.g., Armienti et al., 2007), single-cpx models avoid the additional uncertainty inherent in back-calculating plausible equilibrium liquids. Crystallisation temperatures and pressures were solved iteratively using a single-clinopyroxene thermometer, Eq. 32d in Putirka (2008) but referred to here as Eq. S-2, and single-clinopyroxene barometer for hydrous systems (Eq. 32b of that work, here as Eq. S-3).

Eq. S-2 



Eq. S-3 


This section details the selection criteria for the experimental clinopyroxene-liquid pairs bracketing the Timpe Santa Caterina whole rock (Bryce, 1998) and clinopyroxene compositions (Table S-4) in order to evaluate the accuracy of published clinopyroxene thermobarometric models for alkaline magmas. Experiments containing coexisting clinopyroxene and liquid phases at 0-1.0 GPa were culled from the Library of Experimental Phase Relations (LEPR) database (Hirschmann et al., 2008). Liquid composition constraints consisted of SiO2 = 45–52 wt. %, Al2O3 = 15–20 wt. %, and MgO < 8.1 wt.%, ranges designed to span the potential TSC liquid compositions coexisting with clinopyroxene. Experiments were further culled by limiting clinopyroxene Al2O3 content to <9 wt. % and CaO wt. % to within 2 wt. % of the upper and lower concentrations observed in TSC clinopyroxene (range 18–25 wt. %). This produced a clinopyroxene-liquid dataset of >100 pairs from experimental studies (Hess et al., 1978; Mahood and Baker, 1986; Baker et al., 1987; Sack et al., 1987; Tormey et al., 1987; Gee and Sack, 1988; Kelemen et al., 1990; Kennedy et al., 1990; Sisson and Grove, 1993; Kawamoto, 1996; Métrich and Rutherford, 1998; Wood and Trigila, 2001; Pichavant et al., 2002; Grove et al., 2003; Barclay and Carmichael, 2004; Nekvasil et al., 2004; Di Carlo et al., 2006; Feig et al., 2006; Scoates et al., 2006; Almeev et al., 2007; Villiger et al., 2007; Mercer and Johnston, 2008; Conte et al., 2009).

Table S-6 Ranges of whole rock and clinopyroxene major and minor element compositions (wt. %) observed for the Timpe Santa Caterina flows studied.

LavaClinopyroxene

LowHighLowHigh
SiO246.650.745.851
TiO21.62.10.92.7
Al2O316.819.837.7
FeO*8.210.95.29.2
MnO0.150.1900.19
MgO3.46.31215.6
CaO8.710.920.323.1
Na2O3.75.50.30.8
K2O12.100.02
P2O50.51.400.24
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P-T estimates for TSC clinopyroxene crystallisation based on these models indicate they record a wide range of crustal pressures, from just above the current Moho to the near-surface, with a corresponding temperature range of 1175–1060 °C. Because the barometer requires temperature as an input, sensitivity to temperature was evaluated. Varying barometer input temperatures (obtained from single-cpx thermometer Eq. 32d of Putirka, 2008) by ±50 ºC yields calculated pressures on average 0.12 GPa lower and 0.18 GPa higher, respectively, for these compositions. Undegassed melt H2O content was assumed to be 3 wt. %, after Métrich et al. (2004). However, adopting a H2O input of 2 wt. % generates pressure estimates averaging ~0.05 GPa lower and temperatures ~5 ºC lower than for 3 wt. % H2O.

Figure 1b shows proportions of calculated pressures (n = 287) from single-clinopyroxene thermobarometry of ancient (>80 ka) Etna clinopyroxene compositions of those reported here and previous workers (Tanguy, 1978; Nazzareni et al., 2003; Lopez et al., 2006; Ferlito et al., 2010; Giacomoni et al., 2016).

alphaMELTS v. 1.4 modelling of clinopyroxene trace element content (Fig. S-3)
TSC clinopyroxene trace elements are compared with the evolution of clinopyroxene compositions during cooling of magmas at 1.0, 0.6, and 0.2 GPa. Clinopyroxene fractionating from two mantle melts are shown in Figure S-2: a dry pyroxenite/hydrated (3 wt. % H2O) peridotite melt mixture (solid lines) and a less hydrated (1 wt. % H2O) peridotite melt (dashed lines).

Pyroxenite/peridotite mix composition. A hypothetical melt composition, ‘10pyrper03’, containing 10:90 pyroxenite/peridotite melt was calculated from liquids generated using the alphaMELTS software interface to access the (pH)MELTS family of modelling algorithms. The pyroxenite component was obtained from batch decompression melting of a dry pyroxenite with an average composition from Hyblean pyroxenite xenoliths XIP-4 and XIP-14 reported in Correale et al. (2012). The same melting conditions were applied to a Hyblean peridotite composition (average of xenoliths XIH-1 and XIH-2, Correale et al., 2012) hydrated with 3 wt. % H2O. The pyroxenite and hydrated peridotite both generated 10 % melting at ~1.5 GPa at a pHMELTS input temperature in the 1350–1360 °C range and initial fO2 of NNO+1. The 10:90 ratio was chosen because calculated Y/La concentrations of clinopyroxene coexisting with this melt approximately match the most primitive clinopyroxene in the TSC suite.

Peridotite composition. The hypothetical peridotite melt ‘perid01_20kb’ is the liquid phase produced by 5 % batch decompression melting at 2.0 GPa and 1435 °C using pHMELTS, which is calibrated for pressures between 4 and 1 GPa. It was also chosen for its ability to fractionate clinopyroxene with calculated Y/La similar to TSC clinopyroxene.

To better approximate the likely complex transport, magma replenishment, and crystallisation processes beneath ancient Etna, clinopyroxene compositional evolution in Y/La space was calculated separately as what would fractionate from batch liquids at every decreasing 20 °C temperature step in MELTS. MELTS has been calibrated for pressures at or less than 1.0 GPa and all modelled clinopyroxene compositional paths shown are based on MELTS simulations of magma differentiation (Ghiorso et al., 1995). The alphaMELTS (Smith and Asimow, 2005) default partition coefficients (Kd) of McKenzie and O’Nions (1991) were used for all trace elements in both generating the initial melts and for the isobaric fractionation runs.

Open system behaviour was approximated via a two-step process. First, MELTS batch liquids were generated using the McKenzie and O’Nions Kd values likely relevant to mantle and lower crustal conditions. Second, at each temperature step a hypothetical trace element composition of clinopyroxene instantaneously crystallising from the liquid was calculated using Kds more representative of low pressure partitioning behaviour. Models reported here use the Kds of Hauri et al. (1994) for La and Ce (0.0515 and 0.108 respectively) and Dorais and Tubrett (2008) for Y (0.575), which was calculated for use with the Hauri et al. (1994) Kd values from the partitioning model for clinopyroxene Kds of Wood and Blundy (1997). These are similar to other low pressure Kd datasets reported in Hill et al. (2000) and Laubier et al. (2014), though the choice of a somewhat low value for La is needed to reproduce the highest Y/La of more primitive TSC clinopyroxenes. Generally, the primary difference in the Kd datasets used in these models is the Y partitioning behaviour between clinopyroxene and melt, which is taken to be 0.20 at high pressure and 0.575 at low pressure. Attempts to use the hydrous system model for clinopyroxene Kd values of Sun and Liang (2012), which calculates comparatively low Kd values relative to previously mentioned models and datasets, produced poor fits to TSC clinopyroxene compositions.


Figure S-3 Clinopyroxene trace element evolution during isobaric fractionation of peridotite melt (green) and 10 % pyroxenite component melts (red) at 1.0, 0.6, and 0.2 GPa. Modelling sensitivity to starting composition is illustrated by including paths for melts with 5 % and 20 % pyroxenite component shown as blue and purple dotted lines, respectively.
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The effects of apatite saturation are considered, as whole rock CIPW norm abundances of apatite range from ~1 to 3 % in TSC lavas. Middle rare earth elements (MREE) partition more strongly into apatite than light (L-) and heavy (H-) REE, with Y behaviour being similar to that of HREE. The dominant influence of apatite would be to shift modelled clinopyroxene trace element evolution paths toward lower Ce values. Simple fractional crystallisation modelling of apatite fractionation using the apatite/liquid Kds of Prowatke and Klemme (2006) early from hypothetical hydrated peridotite and mixed component source melts would extend possible compositions directly away from the observed TSC clinopyroxene trends in Y/La vs. Ce space. However, the effects of apatite fractionation on liquids in equilibrium with the most evolved TSC-2 and TSC-7 clinopyroxenes could significantly drive liquids towards lower Ce that could reproduce the TSC-3, TSC-9, and modern Etna clinopyroxene trend. In that scenario, a hydrated peridotite source is not needed and TSC and modern Etna clinopyroxene can be successfully modelled as the products of a mixed hydrated peridotite/10 % pyroxenite source with varying degrees of apatite fractionation during storage and ascent prior to eruption.

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