Collaborative Research: Rheology of Altered Oceanic Lithosphere

蚀变大洋岩石圈的流变性及其在俯冲过程中的演化，在许多过程中起着重要的作用。对俯冲带热模型的解释是边缘俯冲工厂计划的一个目标，取决于对下行板和板-楔形板界面的良好约束。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石脱水，向周围环境释放水，深度超过50-100公里。这些脱水反应被用来解释在某些俯冲带中观察到的双地震带，以及中深度地震事件(50-300公里)的发生。释放的水也可以并入板块上方的地幔楔体中，促进部分上覆地幔的进一步蛇纹岩化，或在火山弧下诱导熔体产生，这取决于P-T条件以及俯冲带和地幔楔体的几何形状。为了了解地震在俯冲带中的分布，重要的是要约束蚀变岩石圈的流变性，它们在脱水反应中如何演化，反应产物的流变性，以及变质反应和下沉板块的输运性质之间的反馈。所有这些问题都是作为边缘孕震带活动的一部分进行探索的。在高压和高温下对蛇纹岩、滑石和细粒橄榄石集合体进行变形实验。实验的目的是：(1)测定蛇纹岩在高温高压下的强度和变形方式，进一步刻画蛇纹岩由脆性变形向塑性变形转变的条件，并首次在实验室测定反蛇纹岩的塑性流变性。这些数据提供了理解改变岩石圈变形和蛇纹岩中流体运输的终端成员力学方面所需的重要约束条件。(2)研究蛇纹岩脱水过程中渗透率、反应进程和流变学之间的反馈关系，以约束可能发生反应诱发地震的条件。(3)限制脱水反应的细粒反应产物(橄榄石滑石水)的流变性。这项实验工作提供了关于蛇纹石脱水过程中释放的水的去向和运输、脱水与地震活动之间的关系以及俯冲过程中相变相关的流变学变化的见解。

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.