Fracture-mediated deep seawater flow and mantle hydration on oceanic transform faults
Fracture-mediated deep seawater flow and mantle hydration on oceanic transform faults
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DOI：
10.1016/j.epsl.2019.115988
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发表时间：
2020-02
影响因子：
5.3
通讯作者：
C. Prigent;J. Warren;A. Kohli;C. Teyssier
中科院分区：
文献类型：
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作者：
C. Prigent;J. Warren;A. Kohli;C. Teyssier
海洋转换断层上的流体-岩石相互作用对岩石圈的变形行为和地球的挥发性循环都具有重要意义。在OTFs中变形和挖掘的岩石保存了有关这些断裂带内流体渗透深度和流体-岩石相互作用性质的信息。在这项研究中，我们重点研究了西南印度脊上的Shaka和Prince Edward OTFs的5条疏浚船，这些疏浚船恢复了大量变形的地幔岩石。样品主要为糜棱岩，在断裂带中变形到高应变，但也含有几代裂缝。根据断裂和剪切带中的矿物组合，结合热压分析，确定了与变形相关的流体-地幔相互作用的三个不同温度范围。在低温（LT）下，这导致蛇纹石（±滑石±角闪石±绿泥石）在< 500-550℃下结晶。在中温（MT）下，绿泥石和角闪石在~ 500-750℃结晶。在高温下，角闪洞（±第二代橄榄岩矿物）结晶。高温裂缝和剪切带中的矿物组成表明，压裂和流体流动至少发生在850-875℃的温度下。将这些结果与两个断层的模拟地热相结合，表明海水渗透延伸至20-25 km深度，蛇纹石化延伸至~ 11-13 km深度。深层流体-岩石相互作用引起的断裂带结构演化以及在OTFs上逐渐形成的LT、MT和HT糜伦岩导致了海洋岩石圈内部的弱化和应变局域化，表明全球转换系统可能代表了地球岩石圈中一个巨大的挥发物储层。
Fluid-rock interaction on oceanic transform faults (OTFs) is important for both the deformation behavior of the lithosphere and volatile cycling in the Earth. Rocks deformed and exhumed at OTFs preserve information about the depth extent of fluid percolation and the nature of fluid-rock interactions within these fault zones. In this study, we focus on five dredges from the Shaka and Prince Edward OTFs on the ultraslow spreading Southwest Indian Ridge that recovered significant volumes of deformed mantle rocks. Samples are predominantly mylonites that have been deformed to high strains in the fault zone, but also contain several generations of fractures. Based on the mineral assemblages in fractures and shear bands combined with thermobarometry analysis, we identified three distinct temperature ranges of fluid-mantle interactions associated with deformation. At low temperature (LT), this leads to crystallization of serpentine (± talc ± amphibole ± chlorite) at <500–550 °C. At medium temperature (MT), chlorite and amphibole crystallized at ∼500–750 °C. At high temperature (HT), amphibole (± second generation peridotitic minerals) crystallized. The composition of minerals in HT fractures and shear bands indicates that fracturing and fluid flow occur up to temperatures of at least 850–875 °C. Combining these results with modeled geotherms for both faults suggests that seawater percolation extended to depths of 20–25 km and that serpentinization extended to ∼11–13 km. The evolution of fault zone structure induced by deep fluid-rock interaction and progressive formation of LT, MT and HT mylonites on OTFs results in weakening and strain localization within the oceanic lithosphere, and suggests that the global transform system may represent a large reservoir of volatiles in the Earth's lithosphere.