英国南安普顿大学 Gernon, Thomas M. 课题组报道了研究裂谷引起的克拉通龙骨断裂驱动金伯利岩火山作用。该研究于2023年7月26日发表于国际一流学术期刊《自然》杂志上。

研究展示了大多数跨越过去 10 亿年的金伯利岩，在大陆分裂后大约 3000 万年(Myr)喷发，表明与裂谷过程有关。研究中的动力学和分析模型表明，在裂谷作用期间，所形成的物理状态下陡峭的岩石圈—软流圈边界(LABs)在软流圈中产生对流不稳定性，缓慢迁移到裂谷带内数百到数千公里处。这些不稳定性在大陆分解后持续了数千万年，并破坏了几十公里厚的克拉通岩石圈（或称龙骨）的稳定性。

在回流中，移位的龙骨被热的、上涌的软流圈和回收的富含挥发物的龙骨的混合物所取代，导致减压部分熔化。研究计算表明，这一过程可以产生少量、低度、富含挥发物的熔体，非常符合金伯利岩的预期特征。总的来说，这些结果通过克拉通龙骨的渐进破坏，提供了金伯利岩喷发和超大陆旋回之间的定量和机械联系。

据悉，金伯利岩富含挥发性物质，曾在过去的地质时期的地表爆发过，偶尔含有金刚石岩浆。这些神秘的岩浆起源于超过150 km深度的地球地幔，出现在稳定的克拉通中，并与超大陆周期大致同步。目前还不清楚它们的活动是由地幔柱还是由克拉通岩石圈的机械弱化所驱动的。

附：英文原文

Title: Rift-induced disruption of cratonic keels drives kimberlite volcanism

Author: Gernon, Thomas M., Jones, Stephen M., Brune, Sascha, Hincks, Thea K., Palmer, Martin R., Schumacher, John C., Primiceri, Rebecca M., Field, Matthew, Griffin, William L., OReilly, Suzanne Y., Keir, Derek, Spencer, Christopher J., Merdith, Andrew S., Glerum, Anne

Issue&Volume: 2023-07-26

Abstract: Kimberlites are volatile-rich, occasionally diamond-bearing magmas that have erupted explosively at Earth’s surface in the geologic past. These enigmatic magmas, originating from depths exceeding 150 km in Earth’s mantle, occur in stable cratons and in pulses broadly synchronous with supercontinent cyclicity. Whether their mobilization is driven by mantle plumes or by mechanical weakening of cratonic lithosphere remains unclear. Here we show that most kimberlites spanning the past billion years erupted about 30 million years (Myr) after continental breakup, suggesting an association with rifting processes. Our dynamical and analytical models show that physically steep lithosphere–asthenosphere boundaries (LABs) formed during rifting generate convective instabilities in the asthenosphere that slowly migrate many hundreds to thousands of kilometres inboard of rift zones. These instabilities endure many tens of millions of years after continental breakup and destabilize the basal tens of kilometres of the cratonic lithosphere, or keel. Displaced keel is replaced by a hot, upwelling mixture of asthenosphere and recycled volatile-rich keel in the return flow, causing decompressional partial melting. Our calculations show that this process can generate small-volume, low-degree, volatile-rich melts, closely matching the characteristics expected of kimberlites. Together, these results provide a quantitative and mechanistic link between kimberlite episodicity and supercontinent cycles through progressive disruption of cratonic keels.

DOI: 10.1038/s41586-023-06193-3

Source: https://www.nature.com/articles/s41586-023-06193-3