澳大利亚麦考瑞大学Chen Chunfei及其团队近日研究揭示了富含碳酸盐的地壳俯冲驱动深层碳和氯循环。2023年8月9日，国际知名学术期刊《自然》发表了这一成果。

新的高压实验表明，富含碳酸盐的地壳岩石中的大多数碳酸盐(> 75 wt%)是主要的俯冲碳库之一，在冷俯冲带和暖俯冲带的脱挥发分和含水熔融中幸存下来，表明它们的俯冲驱动了中元古代以来的深碳循环。研究发现 KCl 和 NaCl 分别成为在温暖和热俯冲带中从氯溶解度低的含水碳酸盐熔体中结晶的稳定相，导致下降板块中固体残余物中的氯被隔离。

因此，在地球历史的中间阶段，富含碳酸盐的岩石的俯冲促进了氯和碳向地幔深处的高效再循环，并导致大气 pCO₂ 下降和自中元古代以来富碳和富氯地幔储层的形成。这个碳和氯的最佳俯冲时期可以解释榴辉岩钻石的年龄和HIMU地幔源区的形成。

据介绍，俯冲到地幔深处和火山喷发到大气中的碳和氯的流量平衡对于我们星球的可居住性至关重要。然而，由于碳和氯在含水条件下具高流动性的特点，俯冲板块流体的普遍流失被认为是切断了碳和氯向地幔深部的输送引起的。

附：英文原文

Title: Carbonate-rich crust subduction drives the deep carbon and chlorine cycles

Author: Chen, Chunfei, Frster, Michael W., Foley, Stephen F., Shcheka, Svyatoslav S.

Issue&Volume: 2023-08-09

Abstract: The flux balances of carbon and chlorine between subduction into the deep mantle and volcanic emissions into the atmosphere are crucial for the habitability of our planet. However, pervasive loss of fluids from subducting slabs has been thought to cut off the delivery of both carbon and chlorine to the deep mantle owing to their high mobility under hydrous conditions. Our new high-pressure experiments show that most carbonates (>75wt%) in carbonate-rich crustal rocks—one of the main subducting carbon reservoirs—survive devolatilization and hydrous melting in cold and warm subduction zones, indicating that their subduction has driven the deep carbon cycle since the Mesoproterozoic. We found that KCl and NaCl, respectively, become stable phases crystallizing from hydrous carbonatite melts with low chlorine solubility in warm and hot subduction zones, resulting in the sequestration of chlorine in the solid residue in downwelling slabs. Accordingly, the subduction of carbonate-rich rocks facilitated highly effective recycling of both chlorine and carbon into the deep mantle at intermediate stages of Earth’s history and led to declining atmospheric pCO₂ and the formation of carbon-rich and chlorine-rich mantle reservoirs since the Mesoproterozoic. This period of optimal carbon and chlorine subduction may explain the ages of eclogitic diamonds and the formation of the HIMU mantle source.

DOI: 10.1038/s41586-023-06211-4

Source: https://www.nature.com/articles/s41586-023-06211-4