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The tungsten-182 record of kimberlites above the African superplume: Exploring links to the core-mantle boundary

Tappe, Sebastian and Budde, Gerrit and Stracke, Andreas and Wilson, Allan and Kleine, Thorsten (2020) The tungsten-182 record of kimberlites above the African superplume: Exploring links to the core-mantle boundary. Earth and Planetary Science Letters, 547 . Art. No. 116473. ISSN 0012-821X. https://resolver.caltech.edu/CaltechAUTHORS:20200722-093725846

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Abstract

Many volcanic hotspots are connected via ‘plume’ conduits to thermochemical structures with anomalously low seismic velocities at the core-mantle boundary. Basaltic lavas from some of these hotspots show anomalous daughter isotope abundances for the short-lived ¹²⁹I-¹²⁹Xe, ¹⁴⁶Sm-¹⁴²Nd, and ¹⁸²Hf-¹⁸²W radioactive decay systems, suggesting that their lower mantle sources contain material that dates back to Earth-forming events during the first 100 million years in solar system history. Survival of such ‘primordial’ remnants in Earth's mantle places important constraints on the evolution and inner workings of terrestrial planets. Here we report high-precision ¹⁸²W/¹⁸⁴W measurements for a large suite of kimberlite volcanic rocks from across the African tectonic plate, which for the past 250 million years has drifted over the most prominent thermochemical seismic anomaly at the core-mantle boundary. This so-called African LLSVP, or ‘large low shear-wave velocity province’, is widely suspected to store early Earth remnants and is implicated as the ultimate source of global Phanerozoic kimberlite magmatism. Our results show, however, that kimberlites from above the African LLSVP, including localities with lower mantle diamonds such as Letseng and Karowe Orapa A/K6, lack anomalous ¹⁸²W signatures, with an average μ¹⁸²W value of 0.0 ± 4.1 (2SD) for the 18 occurrences studied. If kimberlites are indeed sourced from the African LLSVP or superplume, then the extensive ¹⁸²W evidence suggests that primordial or core-equilibrated mantle materials, which may contribute resolvable μ¹⁸²W excesses or deficits, are only minor or locally concentrated components in the lowermost mantle, for example in the much smaller ‘ultra-low velocity zones’ or ULVZs. However, the lack of anomalous ¹⁸²W may simply suggest that low-volume kimberlite magmas are not derived from hot lower mantle plumes. In this alternative scenario, kimberlite magmas originate from volatile-fluxed ambient convecting upper mantle domains beneath relatively thick and cold lithosphere from where previously ‘stranded’ lower mantle and transition zone diamonds can be plucked.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.epsl.2020.116473DOIArticle
ORCID:
AuthorORCID
Tappe, Sebastian0000-0003-1224-5155
Budde, Gerrit0000-0003-0762-779X
Stracke, Andreas0000-0002-9719-4213
Kleine, Thorsten0000-0003-4657-5961
Additional Information:© 2020 Elsevier B.V. Received 21 March 2020, Revised 30 June 2020, Accepted 9 July 2020, Available online 22 July 2020. S.T. and A.W. are supported by the National Research Foundation of South Africa (IPRR and DSI-NRF CIMERA grants). The European Research Council supported S.T. and T.K. through a grant within the Europlanet-2020-Research-Infrastructure program (Europlanet-2020-RI has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 654208). A.S. and T.K. acknowledge funding by the German Research Foundation (DFG Project-ID: 263649064 – TRR 170). We thank Petra Diamonds Ltd, Letseng Diamonds, Lucara Diamonds, Tsodilo Resources, and the De Beers Group of Companies for facilitating sampling at their ground holdings and rock archives. The samples from Tanzania were kindly provided by Richard Brown and the late Barry Dawson. Trond Torsvik is gratefully acknowledged for help with the plate reconstructions and valuable discussions. Helpful comments by Jan Kramers and Katie Smart are truly appreciated. We thank the reviewers Igor Puchtel and Andrea Giuliani for highly constructive comments, and Raj Dasgupta for fair and efficient editorial handling. This is TRR 170 publication number 107. Supplementary information is available in the online version of the paper. Requests for materials should be addressed to S.T. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funders:
Funding AgencyGrant Number
National Research Foundation (South Africa)UNSPECIFIED
European Research Council (ERC)654208
Deutsche Forschungsgemeinschaft (DFG)263649064
Subject Keywords:kimberlite origin; plate tectonics; ultradeep diamonds; primordial mantle reservoirs; LLSVP; extinct radionuclides
Record Number:CaltechAUTHORS:20200722-093725846
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200722-093725846
Official Citation:Sebastian Tappe, Gerrit Budde, Andreas Stracke, Allan Wilson, Thorsten Kleine, The tungsten-182 record of kimberlites above the African superplume: Exploring links to the core-mantle boundary, Earth and Planetary Science Letters, Volume 547, 2020, 116473, ISSN 0012-821X, https://doi.org/10.1016/j.epsl.2020.116473. (http://www.sciencedirect.com/science/article/pii/S0012821X20304179)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104502
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:22 Jul 2020 16:53
Last Modified:22 Jul 2020 16:53

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