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: 1515191
• 负责人: Craig Manning
• 金额: $ 23.97万
• 依托单位: University of California-Los Angeles
• 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 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1515191&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.

该项目涉及在低于~ 300 ℃的温度下地幔橄榄岩与含水流体相互作用的水化、碳酸化和氧化的跨学科研究。 PI将结合对露头和钻孔的联合收割机观测、地球化学分析、结构测量、地质力学实验和数值模拟，以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。实地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、俯冲带上盘的水合作用和碳酸化作用，使蛇绿岩位于变质沉积物之上，以及陆上风化作用。PIs项目将提供匹配的资金和结果，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。PI将继续在压力和温度范围内对地幔楔橄榄岩的俯冲带蚀变进行独立支持的研究，并与调查海底和俯冲相关橄榄岩蚀变的其他小组密切合作，以量化这些不同构造环境中蚀变过程的相似性和差异。橄榄岩蚀变是地球动力学中的一个重要过程。洋壳和地幔的水化作用以及随后的俯冲作用提供了驱动弧火山作用的水，并随着时间的推移调节了地幔的氢含量。在俯冲带的近地表和上盘橄榄岩蚀变过程中形成的碳酸盐是碳循环中一个重要但特征不明显的环节。矿物质的氧化和流体的伴随还原产生H2和烃，以及化学合成微生物的生态位。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，但将转化为橄榄岩蚀变中的平衡和动力学的新兴理解的结果，以及反应驱动的开裂，使我们在这个很少研究的前沿取得突破的边缘。PI将利用阿曼的低温、近地表、活动橄榄岩蚀变来研究输入、输出和原位反应区。这样的研究在具有有限露头和更多降雨的较小橄榄岩暴露中更加困难，在海底热液系统中几乎不可能，并且在古系统的研究中完全不可能。通过250至600米的钻孔进行这种全面的方法是非常罕见的，如果不是前所未有的话。