Seismicity of peridotite alteration

橄榄岩蚀变的地震活动

• 批准号: 2147529
• 负责人: Robert Sohn
• 金额: $ 45.28万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-06-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2147529&HistoricalAwards=false
• 关键词: Seismicity; peridotite; alteration

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.

地幔是在地壳和外核之间发现的一层硅酸盐岩石，占地幔质量的约 67% 和体积的约 84%。地幔岩石很少在地球表面观察到，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，偶尔也暴露在陆地上，地质特征称为蛇绿岩。当橄榄岩暴露于水并与水发生反应时，它会发生化学反应，从而改变岩石和水的成分。这个过程称为蚀变，导致碳从水中转移到岩石中。因此，橄榄岩蚀变是在地球内部封存碳的自然过程。该项目使用在阿曼世界上最大的蛇绿岩进行的独特地震实验的数据，以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博士后助理提供支持。 它促进与阿曼苏丹、捷克共和国和英国的国际合作。 其成果与工程二氧化碳捕获和增强地热系统的应用直接相关。橄榄岩蚀变对于一系列地球科学主题来说是一个极其重要的过程。这些包括弧火山活动、地震过程、碳循环和化学合成生物群落。尽管在露头中经常观察到完全蚀变的橄榄岩（蛇纹岩、橄榄岩、皂石），但目前尚不清楚这是如何发生的，因为蚀变反应通常是自限性的。在大多数地质系统中，蚀变产物会保护反应表面并减少孔隙空间，最终停止蚀变过程。有人提出，反应驱动的裂解——由于地幔岩石蛇纹石化和碳化过程中体积的增加——是通过创建和/或维持持续流体流动的可渗透路径来永久改变蚀变的关键过程。原则上，该过程应产生具有体积变化（各向同性）震源机制成分的非常小的破裂事件。但此类事件从未在现场被观察到。在这里，该团队在正在进行的橄榄岩蚀变地点获得了一个独特的地震数据集，该数据集具有较短的元素间间距（米级）和 1 kHz 采样率，以研究其地震特征。他们确定地震网络检测到的非常小的地震是否代表橄榄岩蚀变产生的裂缝。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）的背景下解释了结果。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大片固体表面上。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。