Fluid processes in subduction zones: two-phase flow numerical simulation and observational constraints

俯冲带是地球表面和内部之间强烈物质交换的地方，因此与广泛的火山活动和地震有关。地球物理流体，特别是水，深深地参与了这一交换过程，但从脱水俯冲岩石圈到表面的流体输送的物理基础仍然是有争议的问题。事实上，已经提出了几种搬运方式（岩墙、底辟、达西型渗流），但它们的影响程度仍有待确定。两相流理论在其新的表述（Bercovici和Ricard 2003）被用来研究水的出溶和渗流对周围基质（俯冲岩石圈和地幔楔）的动力学的后果。在该项目的第一阶段，一个适当的二维代码（流体和岩石基质），包括压实与可变的体积粘度已被开发，和一个孤立的孔隙度波的半解析新的解决方案已被发现基准这样的代码。在包括能量方程和孔隙粘弹性数值模型后，将在适应俯冲带设置的2D几何形状中进行。将研究基质压实和水出溶对地幔楔动力学的影响，从而对弧岩浆生成和水再循环到地幔深部的影响。合作伙伴H.东京工业大学的Iwamori将提供他在俯冲带岩石学方面的专业知识，并专注于水对相变热力学的影响。数值结果将与现有的地震和岩石学数据，特别是日本弧。

Subduction zones are places of intense mass exchange between the Earth’s surface and its interior, and consequently are associated with extensive volcanism and earthquakes. Geophysical fluids, especially water, are deeply involved in this exchange process but the physics underlying the fluid transport from the dehydrating subducting lithosphere to the surface is still matter of debate. Indeed, several modes of transportation (dykes, diapirs, Darcy-type percolation) have been suggested but their degree of implication has still to be determined. The two-phase flow theory in its new formulation (Bercovici and Ricard 2003) is used to investigate the consequence of water exsolution and percolation on the dynamics of the surrounding matrix (subducting lithosphere and mantle wedge). In the first phase of the project an appropriate 2D code (fluid & rocky matrix) including compaction with variable bulk viscosity has been developed, and a semi-analytical new solution of a solitary porosity wave has been found to benchmark such codes. After including the energy equation and poro-viscoelasticity numerical models will be carried out in a 2D geometry adapted to subduction zone settings. The effect of matrix compaction and water exsolution on the mantle wedge dynamics and thus on the arc-magma generation and water recycling into the deep mantle will be studied. The cooperation partner Prof. H. Iwamori of the Tokyo Institute of Technology will provide his expertise on subduction zone petrology and focus on water effects on phase change thermodynamics. Numerical results will be compared to the available seismic and petrological data, especially from the Japanese arc.