Collaborative Research: Deformation-induced Hydration of Peridotite Mylonites in Nature and Experiments

对大洋断裂带的研究表明，流体循环可能驱动这些断裂带浅层脆性部分的弱化和地震破坏。通常认为，当岩石从脆性破裂(断层)过渡到塑性流动(糜棱岩)时，流体循环结束。然而，最近对大洋橄榄岩糜棱岩的分析揭示了普遍存在的含水矿物相。这个项目评估了水在大洋断裂带的脆韧性转变中的循环程度，在那里，地震期间的裂缝传播可以将水向下输送到糜棱岩带。在这个项目中，橄榄岩糜棱岩的分析来自两个相辅相成的背景下的剪切带，大西洋中脊的圣保罗？S岩石和新喀里多尼亚蛇绿岩。研究中使用的方法包括野外工作、显微结构分析、稳定同位素测量和矿物测温。此外，利用实验室岩石变形实验研究了变形过程中流体包裹体的行为，水反应形成水合矿物的化学环境，以及这些水合相在削弱地幔岩石从而局部变形方面的影响。板块构造将水从水圈循环到地幔深处。俯冲的大洋板块将水带到几百公里深，火山作用将水带回地球--S地表。这项研究的重点是如何将水并入大洋中脊海底之下的岩石中，那里的伸展和转换断层与来自浅层岩浆的加热相结合，以驱动海水循环。断层作用为水流创造了通道：在地震周期中，裂缝扩展到断裂带的更深部分，使水能够穿透岩石通常塑性变形的区域。随着时间的推移，这些裂缝会愈合，流体会以大量流体包裹体的形式被困住。该项目研究了这些流体包裹体在长期变形过程中的命运，以及与地幔岩石发生化学反应形成水合矿物的命运，这些矿物充当富水物质的胶囊。当板块最终潜入俯冲带时，这些水将可用于全球循环。这项研究的结果与与水在地球过程中的作用有关的学科有关，包括地震学、岩石学和地球化学、构造学和地球动力学。拟议的研究将通过以下方式推动预期的社会成果：1)妇女充分参与STEM；2)通过对研究生的培训和对本科生的接触，培养一支有竞争力的STEM劳动力队伍；3)通过与新喀里多尼亚地质学家的合作和对新喀里多尼亚社区的公共宣传，增加国际伙伴关系。

Studies of oceanic fault zones have shown that fluid circulation may drive weakening and seismic failure in the shallow brittle part of these faults. It is generally assumed that fluid circulation ends when rocks transition from brittle failure (fault) to plastic flow (mylonite). However, recent analysis of oceanic peridotite mylonites has revealed the ubiquitous presence of hydrous mineral phases. This project assesses the degree to which water circulates though the brittle-ductile transition in oceanic fault zones, where fracture propagation during seismic events can send water downward into mylonite zones. In this project, peridotite mylonites are analyzed from shear zones in two complementary settings, the St. Paul?s Rocks on the Mid-Atlantic Ridge and the New Caledonia ophiolite. Methods used in this research include fieldwork, microstructural analysis, stable isotope measurements, and mineral thermometry. In addition, laboratory rock deformation experiments are used to investigate the behavior of fluid inclusions during deformation, the chemical environment in which water reacts to form hydrous minerals, and the influence these hydrous phases have in weakening mantle rocks and therefore localizing deformation.Plate tectonics cycles water from the hydrosphere to the deep mantle. Subducted oceanic plates drive water to several hundred kilometers depth, and volcanism brings it back to the Earth?s surface. This research focuses on how water is incorporated into rocks beneath the ocean floor at mid-ocean ridges, where extension and transform faulting combine with heating from shallow magma to drive seawater circulation. Faulting creates pathways for water flow: during a seismic cycle, fractures propagate to the deeper part of fault zones, allowing water to penetrate the region where rocks normally deform plastically. These fractures heal over time and the fluids are trapped as numerous fluid inclusions. This project investigates the fate of these fluid inclusions during long-term deformation and chemical reaction with mantle rocks to form hydrous minerals, which act as capsules of water-rich material. When the plate eventually dives into a subduction zone, this water will be available for global circulation. Results of this research are relevant to disciplines that are concerned with the role of water in Earth processes, including seismology, petrology and geochemistry, tectonics, and geodynamics. The proposed study would advance desired societal outcomes through: 1) full participation of women in STEM; 2) development of a competitive STEM workforce through training of graduate students and in-reach efforts to undergraduate students; and 3) increased international partnerships through collaboration with New Caledonian geologists and public outreach to New Caledonian communities.