Collaborative Research: Rheology of Altered Oceanic Lithosphere

蚀变洋岩石圈的流变学及其在俯冲过程中的演化在许多过程中起着重要作用。对俯冲带热模型的解释是边际俯冲工厂计划的一个目标，这取决于对下行板块和板块-楔形界面强度的良好约束。这两种物理性质都可以由蛇纹石的流变学控制。在俯冲过程中，板块压力和温度的增加导致蛇纹岩脱水，向周围环境释放水，深度超过50-100公里。利用这些脱水反应解释了在某些俯冲带观测到的双地震带和中深度地震事件（50-300 km）的发生。释放的水也可以被吸收到板块上方的地幔楔中，根据P-T条件和俯冲带和地幔楔的几何形状，促进部分上覆地幔的进一步蛇纹岩化，或在火山弧下诱发熔体的产生。研究蚀变岩石圈的流变学性质、脱水反应过程中的演化过程、反应产物的流变学性质以及变质反应与俯冲板块输运性质之间的反馈关系，对了解俯冲带地震的分布具有重要意义。所有这些问题都是边缘孕震带倡议的一部分。在高压和高温下，对蛇纹石、滑石和细粒橄榄石集合体进行了变形实验。实验的目的是：(1)确定蛇纹岩在高压和高温下的强度和变形模式，进一步表征由脆性变形向塑性变形转变的条件，并在实验室中首次测量反长岩的塑性流变。这些数据为了解蚀变岩石圈变形和蛇纹岩流体输送的端元力学方面提供了重要的约束条件。(2)研究蛇纹岩脱水过程中渗透率、反应过程和流变性之间的反馈关系，约束可能发生反应诱发地震活动的条件。(3)约束脱水反应细粒反应产物（橄榄石+滑石+水）的流变性能。这项实验工作对蛇纹石脱水过程中释放的水的命运和运移、脱水与地震活动性之间的关系以及俯冲过程中与相变相关的流变学变化提供了深入的见解。

The rheology of altered oceanic lithosphere, and its evolution during subduction, plays an important role in numerous processes. The interpretation of thermal models for subduction zones, a goal of the MARGINS Subduction Factory initiative, depends on good constraints for both the strength of the down-going slab and the slab-wedge interface. Both of these physical properties may be controlled by the rheology of serpentine. The increase in pressure and temperature of the slab during subduction induces the dehydration of serpentine, releasing water to the surrounding environment, at depths greater than 50-100 km. These dehydration reactions are invoked to explain the double-seismic zone observed in some subduction zones, and the occurrence of intermediate depth seismic events (50-300 km). The released water can also be incorporated in the mantle wedge above the slab, promoting further serpentinization of part of the overlying mantle, or inducing melt production under the volcanic arc, depending on P-T conditions and the geometry of the subduction zone and mantle wedge. To understand the distribution of earthquakes in subduction zones it is important to constrain the rheological properties of altered lithosphere, how they evolve during dehydration reactions, the rheology of reaction products, and the feedbacks between metamorphic reactions and transport properties of the down-going slab. All of these issues are being explored as part of the MARGINS Seismogenic Zone initiative.Deformation experiments are being conducted on serpentinites, talc, and fine-grained olivine aggregates at high pressure and temperature. The experiments are designed to: (1) Determine the strength and mode of deformation of serpentinites at high pressure and temperature, to further characterize the conditions of the transition from brittle to plastic deformation, and to measure for the first time the plastic rheology of antigorite if this regime is obtained in the laboratory. These data provide important constraints needed to understand the end-member mechanical aspects of deformation of altered lithosphere and fluid transport in serpentinites. (2) Study the feedbacks between permeability, reaction progress and rheology during dehydration of serpentinites to constrain conditions where reaction induced seismicity may occur. (3) Constrain the rheological properties of the fine-grained reaction products (olivine+talc+water) of dehydration reactions. This experimental work provides insights on the fate and transport of water released during dehydration of serpentine, on the relationship between dehydration and seismicity, and on the changes in rheology associated with phase changes during subduction.