Seismicity of peridotite alteration

地幔是位于地壳和外核之间的一层硅酸盐岩石，占地球质量的67%和体积的84%。地幔岩石在地球表面很少被观察到，因为它们被地壳覆盖着。然而，地幔的上部由橄榄岩组成，通常暴露在海底，偶尔暴露在陆地上，形成一种被称为蛇绿岩的地质特征。当橄榄岩暴露在水中并与水发生反应时，它会发生化学反应，改变岩石和水的成分。这个过程被称为蚀变，导致碳从水中转移到岩石中。因此，橄榄岩的蚀变是一个将碳隔绝在地球内部的自然过程。该项目使用了一项独特的地震实验数据——在阿曼世界上最大的蛇绿岩上进行的——来确定这种自然过程固碳的速度。该项目为伍兹霍尔海洋研究所的一名博士后提供支持。它促进了与阿曼苏丹、捷克共和国和英国的国际合作。其结果与工程二氧化碳捕获和增强型地热系统的应用直接相关。橄榄岩蚀变是一系列地球科学课题的重要过程。这些包括弧火山作用、地震过程、碳循环和化学合成生物群落。虽然在露头中经常观察到完全蚀变的橄榄岩（蛇纹岩、听石岩、肥皂石），但由于蚀变反应通常是自我限制的，因此尚不清楚这是如何发生的。在大多数地质系统中，蚀变产物覆盖了反应表面，减少了孔隙空间，最终停止了蚀变过程。有人提出，反应驱动的裂缝——由于地幔岩石在蛇纹岩化和碳酸化过程中体积的增加——是通过创造和/或维持流体持续流动的渗透性通道而使蚀变永续的关键过程。原则上，这一过程应产生非常小的开裂事件与体积变化（各向同性）的焦点机制组件。但这样的事件从未在现场观察到过。在这里，研究小组获得了一个独特的地震数据集，在一个正在进行的橄榄岩蚀变的地点进行了短元素间距（数量级）和1 kHz采样，以研究其发震特征。他们确定地震台网探测到的非常小的地震是否代表橄榄岩蚀变引起的裂缝。他们在研究地点进行的多学科研究（水文学、岩石学、微生物学）的背景下解释结果。这些结果为水与橄榄岩相互作用时发生的一系列复杂过程提供了新的见解。这些过程发生在地球固体表面的广大区域。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Earth's mantle is a layer of silicate rock found in between the crust and the outer core that represents ~67% of its mass and ~84% of its volume. Mantle rocks are rarely observed on the Earth's surface because they are covered by the crust. Yet, the upper part of the mantle, which is composed of peridotite, is commonly exposed on the seafloor, and occasionally exposed on land in geological features called ophiolites. When peridotite is exposed to, and reacts with, water, it undergoes chemical reactions that change the composition of both the rocks and the water. This process, known as alteration, results in carbon being transferred from the water to the rocks. Peridotite alteration is thus a natural process that sequesters carbon in the Earth's interior. This project uses data from a unique seismic experiment - conducted at the world's largest ophiolite in Oman - to determine how fast this natural process sequesters carbon. The project provides support to a post-doctoral associate at Woods Hole Oceanographic Institution. It fosters international collaboration with the Sultana of Oman, Czech Republic, and the UK. Its outcomes are directly relevant to applications in engineered CO2 capture and enhanced geothermal systems.Peridotite alteration is a fundamentally important process for a spectrum of geoscience topics. These include arc volcanism, earthquake processes, the carbon cycle, and chemosynthetic biological communities. Although fully altered peridotites (serpentinites, listvenites, soapstones) are commonly observed in outcrops, it is unclear how this can happen because alteration reactions are typically self-limiting. In most geological systems alteration products armor reactive surfaces and reduce pore space, which eventually halts the alteration process. It has been proposed that reaction-driven cracking - due to volume increase during serpentinization and carbonation of mantle rocks - is the key process that perpetuates alteration by creating and/or maintaining permeable pathways for continued fluid flow. In principle, this process should generate very small cracking events with volume change (isotropic) focal mechanism components. But such events have never been observed in situ. Here the team acquired a unique seismic dataset with short inter-element spacings (order meters) and 1 kHz sampling at a site of ongoing peridotite alteration to study its seismogenic character. They determine if the very small earthquakes detected by the seismic network represent cracking from peridotite alteration. They interpret the results in the context of the multi-disciplinary studies (hydrology, petrology, microbiology) conducted at the study site. The results provide new insight into the complex set of processes that occur when water interacts with peridotite. These processes occur over vast expanses of the Earth's solid surface.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.