美国麻省理工学院 Murray, Joshua 及其团队近期的研究成果，揭示了通过有机碳保存的蛇绿岩风化能调节古生代的冷却事件。相关论文发表在2023年11月30日出版的《自然—地球科学》杂志上。
该研究团队提供了一个框架，通过蛇绿岩中镁铁质和超镁铁质演示风化引起的有机碳埋藏的增加，来解释古生代冰川作用背后的构造作用力。为了评估蛇绿岩逆冲作用对有机碳埋藏的影响，研究人员将矿物风化模型与碳盒模型相结合。研究发现(超)镁铁质岩石的风化可以通过形成高表面积的蒙脱石粘土，来显著增强有机碳的保存。
理想化的蛇绿岩逆冲引起的有机碳埋藏的增加，导致海洋 δ13C 增加约 3.7 ‰。实验模拟的 δ13C 偏移的时间演化和幅度与古生代的记录相接近。研究人员通过对页岩地球化学特征的分析，揭示了超镁铁质物源区与总有机碳之间的相关性。研究结果表明，在(超)镁铁质岩风化过程中形成的高表面积粘土，对地球的长期碳循环起着重要的控制作用。
据了解，人们普遍认为热带蛇绿岩逆冲与显生宙冰期同期。镁铁质和超镁铁质岩石的暴露也被认为通过增加全球耐候性来触发冷却。然而，每个古生代冰室也与 3-5 ‰ 的 δ13C增加相一致，这被解释为有机碳埋藏的增加，而不是耐候性的增加所引发的。
附：英文原文
Title: Palaeozoic cooling modulated by ophiolite weathering through organic carbon preservation
Author: Murray, Joshua, Jagoutz, Oliver
Issue&Volume: 2023-11-30
Abstract: Ophiolite obductions in the tropics are coeval with Phanerozoic glaciations. The exposure of mafic and ultramafic rocks is thought to trigger cooling by increasing global weatherability. However, each Palaeozoic icehouse also coincides with a δ13C increase of 3-5‰, interpreted as an increase in organic carbon burial, not weatherability. Here we provide a framework that explains the tectonic forces behind Palaeozoic glaciations through increased organic carbon burial caused by the weathering of mafic and ultramafic lithologies in ophiolites. To evaluate the leverage ophiolite obduction has over organic carbon burial, we couple a mineral weathering model with a carbon box model. We show that the weathering of (ultra)mafic rocks can substantially enhance the preservation of organic carbon through the formation of high-surface-area smectite clays. The heightened organic carbon burial induced by an idealized ophiolite obduction causes ocean δ13C to increase by ~3.7‰. The temporal evolution and magnitude of our modelled δ13C excursion approximates Palaeozoic records. We present an analysis of shale geochemistry, which shows a correlation between ultramafic provenance and total organic carbon. Our results indicate that high-surface-area clays, formed during weathering of (ultra)mafic lithologies, exert a major control over Earth’s long-term carbon cycle.
DOI: 10.1038/s41561-023-01342-9
Source: https://www.nature.com/articles/s41561-023-01342-9