2023年10月18日，瑞士伯尔尼大学Timmerman, Suzette及其团队人员在《自然》杂志发表论文，揭示了岩石圈下部的金刚石年龄和超大陆旋回的证据。

研究人员展示了四种同位素系统(Rb-Sr, Sm-Nd, U-Pb和Re-Os)，应用于来自巴西 Juína 和几内亚 Kankan 的13颗岩石圈下金刚石中的铁硫化物和 CaSiO₃ 包裹体，给出了约 4.5 亿至 6.5 亿年前的大致重叠的结晶年龄。冈瓦纳大陆上金刚石矿床的克拉通内位置以及包裹体的年龄、初始同位素比值和微量元素含量，表明其形成于冈瓦纳大陆边缘的俯冲系统。

结合镁铁质地质压力计的结果，研究表明，这些新元古代-古生代岩石圈下的金刚石，在白垩纪冈瓦纳大陆解体之前就一直保存在冈瓦纳大陆之下，证明它们在超大陆迁移过程中增生，并保留在岩石圈龙骨中超过了 300 Myr。研究人员提出，这种岩石圈通过耗尽浮力物质和板块地壳的底辟隆起、金刚石附着在超大陆龙骨上的增长过程，可能增强了超大陆的稳定性。

据研究人员介绍，与古超大陆旋回相关的俯冲作用很少受到地幔样品的约束。岩石圈下的金刚石结晶记录了在 300-700 km 深度的俯冲海洋岩石圈熔体的释放，特别适用于追踪超大陆上深部地幔作用过程的时间和影响。

附：英文原文

Title: Sublithospheric diamond ages and the supercontinent cycle

Author: Timmerman, Suzette, Stachel, Thomas, Koornneef, Janne M., Smit, Karen V., Harlou, Rikke, Nowell, Geoff M., Thomson, Andrew R., Kohn, Simon C., Davies, Joshua H. F. L., Davies, Gareth R., Krebs, Mandy Y., Zhang, Qiwei, Milne, Sarah E. M., Harris, Jeffrey W., Kaminsky, Felix, Zedgenizov, Dmitry, Bulanova, Galina, Smith, Chris B., Cabral Neto, Izaac, Silveira, Francisco V., Burnham, Antony D., Nestola, Fabrizio, Shirey, Steven B., Walter, Michael J., Steele, Andrew, Pearson, D. Graham

Issue&Volume: 2023-10-18

Abstract: Subduction related to the ancient supercontinent cycle is poorly constrained by mantle samples. Sublithospheric diamond crystallization records the release of melts from subducting oceanic lithosphere at 300–700km depths and is especially suited to tracking the timing and effects of deep mantle processes on supercontinents. Here we show that four isotope systems (Rb–Sr, Sm–Nd, U–Pb and Re–Os) applied to Fe-sulfide and CaSiO3 inclusions within 13 sublithospheric diamonds from Juína (Brazil) and Kankan (Guinea) give broadly overlapping crystallization ages from around 450 to 650 million years ago. The intracratonic location of the diamond deposits on Gondwana and the ages, initial isotopic ratios, and trace element content of the inclusions indicate formation from a peri-Gondwanan subduction system. Preservation of these Neoproterozoic–Palaeozoic sublithospheric diamonds beneath Gondwana until its Cretaceous breakup, coupled with majorite geobarometry, suggests that they accreted to and were retained in the lithospheric keel for more than 300Myr during supercontinent migration. We propose that this process of lithosphere growth—with diamonds attached to the supercontinent keel by the diapiric uprise of depleted buoyant material and pieces of slab crust—could have enhanced supercontinent stability.

DOI: 10.1038/s41586-023-06662-9

Source: https://www.nature.com/articles/s41586-023-06662-9