Diamond ascent by rift-driven disruption of cratonic mantle keels
Diamond ascent by rift-driven disruption of cratonic mantle keels
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DOI：
10.21203/rs.3.rs-986686/v1
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发表时间：
2021-12
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影响因子：
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通讯作者：
T. Gernon;Stephen M. Jones;S. Brune;T. Hincks;A. Glerum;A. Merdith;M. Palmer;J. Schumacher;Rebecca M Primiceri;M. Field;W. Griffin;S. O’Reilly;D. Keir;C. Spencer
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作者：
T. Gernon;Stephen M. Jones;S. Brune;T. Hincks;A. Glerum;A. Merdith;M. Palmer;J. Schumacher;Rebecca M Primiceri;M. Field;W. Griffin;S. O’Reilly;D. Keir;C. Spencer
钻石在地球表面以富含挥发性的岩浆形式喷发，称为金伯利岩1，2，3。这些神秘的岩浆起源于地球地幔150公里以上的深处，以稳定的岩浆形式出现，其脉冲与超大陆旋回大致同步。他们的动员是否是由地幔柱5或机械弱化的地幔岩石圈4，6仍不清楚。在这里，我们表明，大多数金伯利岩跨越过去10亿年爆发约2500万年后，大陆分裂的开始，这表明与裂谷过程。我们的动力学模型表明，物理陡峭的岩石圈，软流圈边界形成在终端裂谷（颈缩）产生对流不稳定的软流圈，缓慢迁移数百公里的裂谷内侧，造成不稳定的地幔龙骨几十公里厚。在回流中，被置换的岩石圈被热的上涌的软流圈所取代，导致碳酸盐地幔的部分熔融和岩石圈物质的可变同化。由此产生的小体积金伯利岩岩浆上升迅速，并迅速，exsolving量的二氧化碳（CO2），这是符合独立的constraints7。我们的模型调和诊断金伯利岩的功能，包括关联的岩石圈和地球化学特征，牵连一个共同的软流圈地幔源污染的岩石圈8。总之，这些结果提供了一个定量的和机械的金伯利岩episodicity和超大陆周期之间的联系，通过渐进的破坏的海隆龙骨。
Diamonds are erupted at Earth’s surface in volatile-rich magmas called kimberlites1,2,3. These enigmatic magmas, originating from depths exceeding 150 kilometres in Earth’s mantle1, occur in stable cratons and in pulses broadly synchronous with supercontinent cyclicity4. Whether their mobilization is driven by mantle plumes5 or mechanical weakening of cratonic lithosphere4,6 remains unclear. Here we show that most kimberlites spanning the past billion years erupted approximately 25 million years after the onset of continental fragmentation, suggesting an association with rifting processes. Our dynamic models show that physically steep lithosphere-asthenosphere boundaries formed during terminal rifting (necking) generate convective instabilities in the asthenosphere that slowly migrate many hundreds of kilometres inboard of the rift, causing destabilization of cratonic mantle keel tens of kilometres thick. Displaced lithosphere is replaced by hot, upwelling asthenosphere in the return flow, causing partial melting of carbonated mantle and variable assimilation of lithospheric material. The resulting small-volume kimberlite magmas ascend rapidly and adiabatically, exsolving amounts of carbon dioxide (CO2) that are consistent with independent constraints7. Our model reconciles diagnostic kimberlite features including association with cratons and geochemical characteristics that implicate a common asthenospheric mantle source contaminated by cratonic lithosphere8. Together, these results provide a quantitative and mechanistic link between kimberlite episodicity and supercontinent cycles via progressive disruption of cratonic keels.