Collaborative Research: Alteration of mantle peridotite: Geochemical fluxes and dynamics of far from equilibrium transport

合作研究：地幔橄榄岩的蚀变：地球化学通量和远离平衡传输的动力学

• 批准号: 1513714
• 负责人: James Hirth
• 金额: $ 18.45万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1513714&HistoricalAwards=false
• 关键词: Collaborative; Research; Alteration; mantle; peridotite

This project involves an interdisciplinary study of hydration, carbonation and oxidation of mantle peridotite interacting with aqueous fluids at temperatures below ~ 300C. The PIs will combine observations of outcrops and boreholes, geochemical analyses, structural measurements, geomechanical experiments and numerical modeling to investigate feedback between alteration and fluid transport, and to quantify the resulting geochemical fluxes. Field observations and sampling will take place mainly in the Samail ophiolite of Oman, where peridotite has undergone spreading-ridge-related hydrothermal alteration, hydration and carbonation in the hanging-wall of the subduction zone that emplaced the ophiolite over metasediments, and subaerial weathering. The PIs project will provide matching funds and results that dovetail with the 2015-2018 International Continental Scientific Drilling Program (ICDP) Oman Drilling Project, and the many other related efforts just getting underway. The PIs will continue their independently supported research on subduction zone alteration of mantle wedge peridotites at a range of pressures and temperatures, and work closely with other groups investigating seafloor and subduction-related peridotite alteration, in order to quantify the similarities and differences in alteration processes in these different tectonic environments. They will generalize their results to global alteration processes and geochemical cycles.Alteration of peridotite is an essential process in Earth dynamics. Hydration of oceanic crust and mantle, followed by subduction, supplies water to drive arc volcanism, and modulates the hydrogen content of the mantle over time. Carbonate formation during alteration of peridotite, near the surface and in the hanging wall in subduction zones, is an important but poorly characterized link in the carbon cycle. Oxidation of minerals and concomitant reduction of fluids produces H2 and hydrocarbons, and a niche for chemosynthetic microbes. Chemical weathering is as important as magmatism and plate tectonics in shaping the Earths surface. The interplay of chemical and physical mechanisms of peridotite alteration is not well understood, but will be transformed as a result of emerging understanding of equilibria and kinetics in peridotite alteration, and reaction-driven cracking that has left us poised on the brink of a breakthrough at this little-studied frontier. The PIs will take advantage of low temperature, near surface, active peridotite alteration in Oman to study inputs, outputs, and the reaction zone in situ. Such a study is more difficult in smaller peridotite exposures with limited outcrop and more rainfall, nearly impossible in submarine hydrothermal systems, and completely impossible in studies of ancient systems. Such a comprehensive approach via 250 to 600 meter boreholes is very rare, if not unprecedented.

该项目涉及对地幔橄榄岩与温度低于 300C 的含水流体相互作用的水化、碳化和氧化的跨学科研究。 PI 将结合露头和钻孔的观测、地球化学分析、结构测量、地质力学实验和数值模拟来研究蚀变和流体输送之间的反馈，并量化由此产生的地球化学通量。现场观测和取样将主要在阿曼的萨迈伊蛇绿岩进行，那里的橄榄岩经历了与扩张脊相关的热液蚀变、俯冲带上盘的水化和碳化作用，将蛇绿岩置于变沉积物之上，以及地下风化作用。 PIs项目将提供与2015-2018年国际大陆科学钻探计划（ICDP）阿曼钻探项目以及许多其他正在进行的相关工作相吻合的配套资金和成果。 PI 将继续其独立支持的关于在一定压力和温度下地幔楔橄榄岩俯冲带蚀变的研究，并与其他研究海底和俯冲相关橄榄岩蚀变的小组密切合作，以量化蚀变过程的异同在这些不同的构造环境中。他们将把他们的结果推广到全球蚀变过程和地球化学循环。橄榄岩的蚀变是地球动力学的一个重要过程。洋壳和地幔的水合作用以及随后的俯冲作用，提供水来驱动弧火山活动，并随着时间的推移调节地幔的氢含量。俯冲带地表附近和上盘的橄榄岩蚀变过程中碳酸盐的形成是碳循环中一个重要但特征不明确的环节。矿物质的氧化和伴随的液体的还原产生氢气和碳氢化合物，并为化学合成微生物提供了一个生态位。在塑造地球表面方面，化学风化与岩浆作用和板块构造一样重要。橄榄岩蚀变的化学和物理机制的相互作用尚不清楚，但由于对橄榄岩蚀变的平衡和动力学的新认识，以及反应驱动的裂解，这将使我们处于突破的边缘，从而发生转变。这个很少有人研究的前沿领域。 PI 将利用阿曼的低温、近地表、活跃的橄榄岩蚀变来研究输入、输出和原位反应区。这样的研究在较小的橄榄岩暴露、露头有限和降雨较多的情况下更加困难，在海底热液系统中几乎不可能，在古代系统的研究中完全不可能。这种通过 250 至 600 米钻孔进行的综合方法即使不是史无前例的，也是非常罕见的。