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.

该项目涉及地幔橄榄岩在低于~300℃的温度下与水流体相互作用的水化、碳化和氧化的跨学科研究。PIS将结合露头和钻孔观测、地球化学分析、构造测量、地质力学实验和数值模拟，以调查蚀变和流体运移之间的反馈，并量化由此产生的地球化学通量。野外观察和取样将主要在阿曼的Samail蛇绿岩中进行，那里的橄榄岩经历了与扩张脊有关的热液蚀变、俯冲带上盘的水化和碳酸盐化作用，蛇绿岩侵位于变质岩之上，以及地表风化作用。PIS项目将提供与2015-2018年国际大陆科学钻探计划(ICDP)阿曼钻探项目相匹配的资金和成果，以及刚刚开始的许多其他相关努力。PIS将继续在一定压力和温度范围内对地幔楔形橄榄岩的俯冲带蚀变进行独立支持的研究，并与其他研究海底和与俯冲有关的橄榄岩蚀变的小组密切合作，以量化这些不同构造环境中蚀变过程的异同。他们将把他们的结果推广到全球的蚀变过程和地球化学循环。橄榄岩的蚀变是地球动力学中的一个基本过程。洋壳和地幔的水化作用，然后是俯冲，为驱动弧形火山活动提供了水，并随着时间的推移调节了地幔的氢含量。在俯冲带近地表和上盘橄榄岩蚀变过程中，碳酸盐的形成是碳循环中一个重要但缺乏特征的环节。矿物的氧化和随之而来的流体的还原产生了氢气和碳氢化合物，并为化学合成微生物创造了一个生态位。在形成地球表面的过程中，化学风化作用与岩浆作用和板块构造作用一样重要。橄榄岩蚀变的化学和物理机制之间的相互作用尚不清楚，但随着对橄榄岩蚀变平衡和动力学的新认识以及反应驱动的裂解的出现，橄榄岩蚀变的化学和物理机制的相互作用将被改变，这使我们有望在这一鲜有研究的前沿取得突破。PIS将利用阿曼低温、近地表、活跃的橄榄岩蚀变来研究投入、产出和原地反应带。这样的研究在露头有限、降雨量较多的较小的橄榄岩暴露中更加困难，在海底热液系统中几乎是不可能的，在古代系统的研究中完全不可能。这种通过250到600米的钻孔进行综合施工的方法即使不是史无前例的，也是非常罕见的。