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

本项目涉及到地幔橄榄岩在低于~ 300℃的温度下与水流体相互作用的水化、碳酸化和氧化的跨学科研究。pi将结合露头和钻孔观测、地球化学分析、结构测量、地质力学实验和数值模拟，调查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。野外观察和取样将主要在阿曼的Samail蛇绿岩进行，那里的橄榄岩经历了与伸展脊有关的热液蚀变、俯冲带上壁上的水化和碳酸化作用，蛇绿岩被置于变质沉积层上，并经历了陆上风化作用。PIs项目将提供与2015-2018年国际大陆科学钻井计划（ICDP）阿曼钻井项目相匹配的资金和结果，以及许多其他正在进行的相关工作。pi将继续独立支持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蚀变过程和地球化学旋回。橄榄岩蚀变是地球动力学的一个重要过程。海洋地壳和地幔的水化作用，以及随后的俯冲作用，为弧火山活动提供了水，并随着时间的推移调节了地幔的氢含量。俯冲带近地表和上盘橄榄岩蚀变过程中的碳酸盐形成是碳循环中一个重要但特征不明显的环节。矿物氧化和伴随的流体还原产生H2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的相互作用还没有得到很好的理解，但随着对橄榄岩蚀变平衡和动力学的新认识的出现，以及反应驱动的裂缝，我们将在这个很少研究的前沿突破的边缘保持平衡。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。这种研究在较小的橄榄岩暴露、有限的露头和更多的降雨中更加困难，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 - 600米钻孔的综合方法即使不是史无前例的，也是非常罕见的。

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.