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A secretive mechanical exchange between mantle and crustal volatiles revealed by helium isotopes in 13C-depleted diamonds

S. Mikhail1,

1The School of Earth and Environmental Sciences, University of St. Andrews, UK

J.C. Crosby1,

1The School of Earth and Environmental Sciences, University of St. Andrews, UK

F.M. Stuart2,

2Isotope Geosciences Unit, Scottish Universities Environmental Research Centre, UK

L. DiNicola2,

2Isotope Geosciences Unit, Scottish Universities Environmental Research Centre, UK

F.A.J. Abernethy3

3Department of Physical Sciences, The Open University, UK

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Mikhail, S., Crosby, J.C., Stuart, F.M., DiNicola, L., Abernathy, F.A.J. (2019) A secretive mechanical exchange between mantle and crustal volatiles revealed by helium isotopes in 13C-depleted diamonds. Geochem. Persp. Let. 11, 39–43.

SM acknowledges support from the National Environmental Research Council (grant no. NE/PO12167/1).

Geochemical Perspectives Letters v11  |  doi: 10.7185/geochemlet.1923
Received 23 April 2019  |  Accepted 28 August 2019  |  Published 10 October 2019
Copyright © The Authors

Published by the European Association of Geochemistry
under Creative Commons License CC BY-NC-ND 4.0




Table 1 Data for southern African diamondites. A full data table including all comparative data is located in the Supplementary Information (Table S-1).
SampleLocationParaMineralsR/Ra±4He ccSTP/g3He ccSTP/gδ13C (‰)±N at.ppmδ15N (‰)±
DIA030SAWGnt8.50.41.33 E-071.51 E-12-16.60.28+6.43.9
DIA053SAWGnt2.80.73.20 E-081.18 E-13-20.80.556+2.00.7
DIA057B#1SA0.10.06.79 E-075.81 E-14-21.40.11389
DIA057B#2SA0.10.16.90 E-071.25 E-13-21.40.11389
DIA058BSAEGnt3.90.27.42 E-083.84 E-13-19.10.1
DIA059SAWGnt0.50.21.42 E-071.01 E-13-22.20.313+5.36.1
DIA073BSAWGnt1.90.48.71 E-082.21 E-13-17.40.12812+6.90.5
DIA077SA7.40.51.44 E-071.43 E-12
ORF9OrapaWGnt2.44 E-08-5.30.1
ORF12Orapa6.72 E-08
ORF19OrapaEGnt4.22.79.02 E-085.11 E-13-8.00.1255+5.80.1
ORF26#1OrapaP + ECpx + Gnt4.22 E-09-14.60.238-4.92.2
ORF26#2OrapaP + ECpx + Gnt-17.80.219+23.26.6
ORF28#1Orapa5.37 E-08-4.30.1775+2.90.2
ORF28#2Orapa-4.90.252+19.70.6
ORF41Orapa7.77 E-08-14.80.31146+14.70.2
ORF57OrapaEGnt7.50.72.24 E-072.26 E-12-16.60.217+18.43.0
ORF60OrapaChromite-6.50.11054+12.10.2
ORF91Orapa-20.30.3401+4.40.3
ORF143OrapaEGnt1.61.11.03 E-072.17 E-13-19.90.2647+10.00.2

Abbreviations: W = websteritic, P = peridotitic, E = eclogitic, Gnt = garnet, Cpx = clinopyroxene, SA = southern Africa.

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Figure 1 New C and N isotope data for southern African diamondites (red circles) and literature data (grey circles: Gautheron et al., 2005

Gautheron, C., Cartigny, P., Moreira, M., Harris, J.W., Allégre, C.J. (2005) Evidence for a mantle component shown by rare gases, C and N isotopes in polycrystalline diamonds from Orapa (Botswana). Earth and Planetary Science Letters 240, 559–572.

; Burgess et al., 1998

Burgess, R., Johnson, L., Mattey, D., Harris, J., Turner, G. (1998) He, Ar and C isotopes in coated and polycrystalline diamonds. Chemical Geology 146, 205–217.

) Fields are shown for other diamondites (Mikhail et al., 2013

Mikhail, S., Kurat, G., Dubosi, G., Verchovsky, A.B., Jones, A.P., Mileage, H.J. (2013) Peridotitic and websteritic diamondites provide new information regarding mantle melting and metasomatism induced through the subduction of crustal volatiles. Geochimica Cosmochimica et Acta 107, 1–11.

), eclogitic monocrystalline diamonds from Jwaneng (Cartigny et al., 1998

Cartigny, P., Harris, J.W., Javoy, M. (1998) Eclogitic diamond formation at Jwaneng: no room for a recycled component. Science 280, 1421–1424.

) and Orapa (Cartigny et al., 1999

Cartigny, P., Harris J.W., Javoy M. (1999) Eclogitic, peridotitic and metamorphic diamonds and the problems of carbon recycling—the case of Orapa (Botswana). 7th International Kimberlite Conference Extended Abstracts, 117–124.

), the mean mantle and altered oceanic crustal material (Cartigny et al., 2014

Cartigny, P., Palot, M., Thomassot, E., Harris, J.W. (2014) Diamond formation: A stable isotope perspective. Annual Reviews of Earth and Planetary Sciences 42, 699–732.

).
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Figure 2 (a) Helium isotope systematics of fluids released by in vacuo crushing of diamondites. The 3He/4He of modern the convecting upper mantle (CUM) and the sub-continental lithospheric mantle (SCLM) are shown for reference. (b) Carbon-helium isotope systematics of southern African diamondites and fibrous diamonds from across southern Africa. The mixing lines are plotted between mantle and crustal fluid sources, the crosses refer to percent of mantle fluid component. The mixing lines plotted in Figure 2b are hyperbolic as [4He]mantle/[4He]crust is assumed to be 10. Comparative data are from Burgess et al. (1998)

Burgess, R., Johnson, L., Mattey, D., Harris, J., Turner, G. (1998) He, Ar and C isotopes in coated and polycrystalline diamonds. Chemical Geology 146, 205–217.

, Gautheron et al. (2005)

Gautheron, C., Cartigny, P., Moreira, M., Harris, J.W., Allégre, C.J. (2005) Evidence for a mantle component shown by rare gases, C and N isotopes in polycrystalline diamonds from Orapa (Botswana). Earth and Planetary Science Letters 240, 559–572.

and Timmermann et al. (2018

Timmermann, S., Honda, M., Phillips, D., Jaques, A.L., Harris, J.W. (2018) Noble gas geochemistry of fluid inclusions in South African diamonds: implications for the origin of diamond-forming fluids. Mineralogy and Petrology 112, 181–195.

, 2019a

Timmermann, S., Yeowa, H., Honda, M., Howell, D., Jaquesa, A.L., Krebs, M.Y., Woodland, S., Pearson, D.G., Ávila, Y.A., Ireland, T.R. (2019a) U-Th/He systematics of fluid-rich ‘fibrous’ diamonds – Evidence for pre- and syn-kimberlite eruption ages. Chemical Geology 515, 22–36.

).
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Figure 3 Cartoon illustrating the model discussed in the text. Not to scale.
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