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Kimberlites reveal 2.5-billion-year evolution of a deep, isolated mantle reservoir

Woodhead, Jon; Hergt, Janet; Giuliani, Andrea; Maas, Roland; Phillips, David; Pearson, D. Graham; Nowell, Geoff

Kimberlites reveal 2.5-billion-year evolution of a deep, isolated mantle reservoir Thumbnail


Authors

Jon Woodhead

Janet Hergt

Andrea Giuliani

Roland Maas

David Phillips

D. Graham Pearson



Abstract

The widely accepted paradigm of Earth's geochemical evolution states that the successive extraction of melts from the mantle over the past 4.5 billion years formed the continental crust, and produced at least one complementary melt-depleted reservoir that is now recognized as the upper-mantle source of mid-ocean-ridge basalts1. However, geochemical modelling and the occurrence of high 3He/4He (that is, primordial) signatures in some volcanic rocks suggest that volumes of relatively undifferentiated mantle may reside in deeper, isolated regions2. Some basalts from large igneous provinces may provide temporally restricted glimpses of the most primitive parts of the mantle3,4, but key questions regarding the longevity of such sources on planetary timescales—and whether any survive today—remain unresolved. Kimberlites, small-volume volcanic rocks that are the source of most diamonds, offer rare insights into aspects of the composition of the Earth’s deep mantle. The radiogenic isotope ratios of kimberlites of different ages enable us to map the evolution of this domain through time. Here we show that globally distributed kimberlites originate from a single homogeneous reservoir with an isotopic composition that is indicative of a uniform and pristine mantle source, which evolved in isolation over at least 2.5 billion years of Earth history—to our knowledge, the only such reservoir that has been identified to date. Around 200 million years ago, extensive volumes of the same source were perturbed, probably as a result of contamination by exogenic material. The distribution of affected kimberlites suggests that this event may be related to subduction along the margin of the Pangaea supercontinent. These results reveal a long-lived and globally extensive mantle reservoir that underwent subsequent disruption, possibly heralding a marked change to large-scale mantle-mixing regimes. These processes may explain why uncontaminated primordial mantle is so difficult to identify in recent mantle-derived melts.

Journal Article Type Article
Acceptance Date Jul 29, 2019
Online Publication Date Sep 25, 2019
Publication Date Sep 26, 2019
Deposit Date Oct 29, 2019
Publicly Available Date Mar 25, 2020
Journal Nature
Print ISSN 0028-0836
Electronic ISSN 1476-4687
Publisher Nature Research
Peer Reviewed Peer Reviewed
Volume 573
Issue 7775
Pages 578-581
DOI https://doi.org/10.1038/s41586-019-1574-8
Public URL https://durham-repository.worktribe.com/output/1286431

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