RII Track-4: Investigating the Effects of Faulting on Chemical Exchange Between Seawater and Earth’s Mantle at Slow Mid-Ocean Ridges

大洋中脊系统是一个65,000公里长的山脉，在每个大洋盆地的中心环绕着地球。新的构造板块沿着山脊以每年1-20厘米的速度不断产生。在地质时间尺度上，通过海水渗入大洋中脊的热岩时发生的化学反应和从大陆河流系统流入海洋的盐分之间的平衡，维持全球海水组成，从而维持地球气候。地幔岩石的化学和矿物组成与地壳岩石截然不同，其与海水的化学相互作用的性质以及对海水组成的更大影响，人们知之甚少。这项提议的目标是增进对海底地幔-岩石暴露破裂以允许海水渗透的过程的了解，从而促进全球大洋中脊系统大约一半的水-岩石化学交换。这项研究的结果将被整合到本宁顿学院的本科地球科学课程和本宁顿学院本科生的独立研究项目中。该项目的目标是了解先前存在的韧性变形组构和地幔橄榄岩暴露的构造环境如何控制岩石在脆性破裂过程中产生渗透性的过程。将使用几种不同类型的断裂带对大西洋中脊(MAR)沿线三个地幔橄榄岩露出的岩石样品进行研究：1)将使用微型计算机断层扫描和扫描电子显微镜成像来表征断裂网络的微观几何形状；2)将使用热重分析和氦气化学计量来量化热液蚀变的程度；3)将使用共聚焦拉曼光谱通过对蚀变矿物和捕获流体的微观分析来进一步限制热液交换的性质。岩石样本将从伍兹霍尔海洋研究所和德国不来梅的不来梅核心储存库获得。这项研究的成果将在理解深层生物圈、地球上潜在的生命起源以及其他星球上潜在的生命宿主方面具有广泛的应用。这一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 mid-ocean ridge system is a 65,000 km-long mountain range that wraps around the Earth at the center of each ocean basin. New tectonic plate is continuously generated along the ridges at rates of one to 20 cm per year. Global seawater composition, and thus Earth’s climate, is maintained over geologic timescales by a balance between chemical-exchange reactions that occur when seawater infiltrates into hot rock at mid-ocean ridges, and salts flowing into the ocean from continental rivers systems. Mantle rock has a radically different chemical and mineral composition than crustal rock, and the nature of its chemical interactions with seawater, along with the larger implications for seawater composition, are poorly understood. The goal of this proposal is to build understanding of the processes by which seafloor mantle-rock exposures are fractured to permit seawater infiltration, and thus facilitate water-rock chemical exchange on roughly half of the global mid-ocean ridge system. Results from this study will be integrated in the undergraduate Earth Science courses and independent research projects for undergraduate students at Bennington College, a small liberal arts institution.The goals of this project are to understand how pre-existing ductile deformation fabrics and the tectonic environment of mantle peridotite exposures control the process by which rock permeability is generated during brittle fracturing. Rock samples collected from three mantle peridotite exposures along the Mid-Atlantic Ridge (MAR) that formed by very different types of fault zones will be examined using several distinct microanalysis and imaging techniques: 1) micro-computed tomography and scanning electron microscope imaging will be used to characterize the micro-scale geometry of fracture networks, 2) thermogravimetric analysis and helium gas pycnometry will be used to quantify the degree of hydrothermal alteration and 3) confocal Raman spectroscopy will be used to place additional constraints on the nature of hydrothermal exchange with micro-analysis of alteration minerals and trapped fluids. Rock samples will be obtained from collections at Woods Hole Oceanographic Institution and from the Bremen Core Repository in Bremen, Germany. The outcomes of this research will have broad applications to understanding the deep biosphere, and potential origins of life on Earth as well as potential hosts for life on other planets.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.