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

合作研究：自然界和实验中橄榄岩糜棱岩变形引起的水化

• 批准号: 1347309
• 负责人: Christian Teyssier
• 金额: $ 14.17万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-04-01 至 2018-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1347309&HistoricalAwards=false
• 关键词: Collaborative; Research; Deformation; induced; Hydration

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.

对海洋断裂带的研究表明，流体循环可能会导致这些断裂带浅层脆性部分的弱化和地震破坏。一般认为，当岩石从脆性破坏（断层）转变为塑性流动（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含水矿物相的普遍存在。该项目评估了水在海洋断裂带中通过脆-韧性过渡循环的程度，地震事件期间断裂扩展可将水向下送入糜棱岩带。在这个项目中，橄榄岩糜棱岩分析剪切带在两个互补的设置，圣保罗？中大西洋海岭的岩石和新喀里多尼亚蛇绿岩。研究方法包括野外工作、显微构造分析、稳定同位素测量和矿物测温。此外，实验室岩石变形实验也被用来研究流体包裹体在变形过程中的行为，水反应形成含水矿物的化学环境，以及这些含水相在弱化地幔岩石从而使变形局部化方面的影响。板块构造使水从水圈循环到深部地幔。俯冲的海洋板块将水带到几百公里深的地方，火山活动又将水带回地球？s表面。这项研究的重点是水是如何融入洋中脊海底岩石的，在那里，伸展和转换断层联合收割机与浅层岩浆的加热相结合，推动海水循环。断层为水流创造了通道：在地震周期中，裂缝传播到断层带的较深部分，使水能够渗透到岩石通常塑性变形的区域。这些裂缝随着时间的推移而愈合，并且流体被捕获为许多流体包裹体。该项目研究这些流体包裹体在长期变形和与地幔岩石发生化学反应以形成含水矿物的过程中的命运，这些含水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。这项研究的结果与关注水在地球过程中的作用的学科有关，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促进预期的社会成果：1）妇女充分参与STEM; 2）通过培训研究生和深入本科生的努力，发展一支有竞争力的STEM工作队伍; 3）通过与新喀里多尼亚地质学家合作和向新喀里多尼亚社区进行公众宣传，加强国际伙伴关系。