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

大洋中脊系统是一条65，000公里长的山脉，在每个海洋盆地的中心环绕地球。新的构造板块沿着海脊以每年1至20厘米的速度不断生成。全球海水的组成，以及地球的气候，在地质时间尺度上是通过海水渗入大洋中脊的热岩时发生的化学交换反应和从大陆河流系统流入海洋的盐之间的平衡来维持的。地幔岩的化学和矿物成分与地壳岩完全不同，其与海水的化学相互作用的性质以及对海水成分的更大影响沿着也知之甚少。该提案的目标是了解海底地幔岩石暴露破裂以允许海水渗透的过程，从而促进全球洋中脊系统大约一半的水-岩石化学交换。本研究的结果将被整合到本宁顿学院（一个小型文科院校）的本科生地球科学课程和独立研究项目中，该项目的目标是了解预先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渗透性在脆性断裂过程中产生的过程。将使用几种不同的微分析和成像技术对从沿着大西洋中脊（MAR）的三个地幔橄榄岩暴露区采集的岩石样本进行检查，这些地幔橄榄岩暴露区由非常不同类型的断层带形成：1）微计算机断层摄影和扫描电子显微镜成像将用于表征裂缝网络的微观尺度几何形状，2）热重分析和氦气比重计将用于量化热液蚀变的程度，3）共焦拉曼光谱将用于对与微-蚀变矿物和圈闭流体分析。岩石样本将从伍兹霍尔海洋研究所和德国不莱梅的不莱梅核心储存库中采集。这项研究的成果将有广泛的应用，以了解深层生物圈，地球上生命的潜在起源以及其他行星上生命的潜在宿主。该奖项反映了NSF的法定使命，并已被认为是值得支持的，通过评估使用基金会的知识价值和更广泛的影响审查标准。

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.