Seismicity of peridotite alteration

地幔是位于地壳和外核之间的一层硅酸盐岩石，占其质量的67%和体积的84%。地幔岩石很少在地球表面被观测到，因为它们被地壳覆盖。然而，由橄榄岩组成的地幔上部通常暴露在海底，偶尔在陆地上暴露在被称为蛇绿岩的地质特征中。当橄榄岩暴露在水中并与水反应时，它会经历化学反应，改变岩石和水的成分。这一过程被称为蚀变，导致碳从水中转移到岩石中。因此，橄榄岩的改变是一个自然的过程，它将碳封存在地球内部。该项目使用在阿曼世界上最大的蛇绿岩上进行的独特地震实验的数据来确定这个自然过程封存碳的速度有多快。该项目为伍兹霍尔海洋研究所的一名博士后助理提供支持。它促进了与阿曼苏丹、捷克共和国和英国的国际合作。它的结果直接关系到工程二氧化碳捕获和增强型地热系统的应用。橄榄岩蚀变是一系列地球科学课题的根本重要过程。其中包括弧形火山作用、地震过程、碳循环和化学合成生物群落。虽然完全蚀变的橄榄岩(蛇纹岩、斜长岩、皂石)在露头中很常见，但这是如何发生的还不清楚，因为蚀变反应通常是自我限制的。在大多数地质系统中，蚀变产物装甲反应表面，减少孔隙空间，最终停止蚀变过程。有人提出，由于地幔岩石在蛇纹岩和碳酸盐化过程中体积增加，反应驱动的破裂是通过建立和/或保持持续流体流动的渗透通道而使蚀变永久化的关键过程。原则上，这一过程应该产生具有体积变化(各向同性)震源机制成分的非常小的破裂事件。但这样的事件从未在现场观察到过。在这里，研究小组在一个正在进行橄榄岩蚀变的地点获得了一个独特的地震数据集，具有较短的元素间间隔(数量级米)和1 kHz的采样，以研究其地震孕育特征。他们确定地震台网探测到的极小地震是否代表橄榄岩蚀变产生的裂缝。他们在研究现场进行的多学科研究(水文学、岩石学、微生物学)的背景下解释了结果。这些结果提供了对水与橄榄岩相互作用时发生的一系列复杂过程的新见解。这些过程发生在地球上广阔的固体表面上。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.