Dynamical coupling of deformation and melt transport in the Earth: A combined theoretical and experimental study

板块构造仍然是固体地球地球物理最重要的背景，它描述了固体地球表面通过14个刚性板块沿弱边界相互作用的相对运动而产生的运动。这些边界提供了地球上大多数地震和火山的位置和相对运动的轨迹，尽管板块构造很好地描述了它们的位置和相对运动，但它们的动力学和性质仍然知之甚少。然而，板块边界的一个关键特征是，它们中的许多是具有活火山作用的岩浆，可能是熔岩(岩浆)与其固体宿主的相互作用可以导致必要的结构和软弱保持板块边界。PI和其他人的实验室实验表明，部分熔融岩石的变形可以导致自发地局部化进入富含熔体的网络，从而削弱岩石并为热量和熔体传输提供有效的途径。因此，了解部分熔融体系的动力学对于了解板材边界的行为和演化至关重要。这个项目的目的是推进我们对这一过程的理论理解，以便将实验结果外推到地球上的各种条件下。部分熔岩在扭转变形过程中存在着大量的高压和高温实验数据，从这些数据中可以推断出许多关于应力驱动偏析的活跃机制的信息。这个项目的重点是为这些实验开发更好的理论和计算模型。我们并行使用两种方法对过程进行建模，并将模型与实验进行比较。第一种是建立偏微分方程组的数值模型，该偏微分方程组来源于两相流或岩浆动力学理论，在扭转变形几何中求解。这项工作的一个副产品将是开发和发布一个用于一般多物理问题的先进计算系统。待测试的效应将包括基质变形的各种本构模型以及表面能和损伤的各种效应。第二种方法是在非平衡热力学框架内开发有效的宏观本构模型，使用一种在冶金学中已经很成熟但刚刚开始应用于地球科学的形式主义。这种方法用“内部状态变量”来描述材料的结构特征，并跟踪与之相关的储存和耗散的能量。其结果将是热力学上一致的本构方程，可以在地球动力学模型中求解，这些模型探索在长度尺度上发生的应力驱动的分离的大规模影响，其规模比地球动力学模型中可以求解的要小得多。这个有效的本构模型还将包括熔体传输特性，以便可以在俯冲带、山脊、裂谷和其他行星环境中探索变形和流体流动之间耦合的潜在后果。

Plate tectonics remains the over-arching context for solid earth geophysics and describes the motion of the solid Earth's surface by the relative movement of ~14 rigid plates that interact along weak boundaries. These boundaries provide the locus for most of the planet's earthquakes and volcanoes and while their location and relative motions are well described by plate tectonics, their dynamics and properties remain poorly understood. A key feature of plate boundaries, however, is that many of them are magmatic with active volcanism and it may be that the interaction of molten rock (magma) with its solid host can lead to the necessary structures and weakness preserving plate boundaries. Laboratory experiments by the PI and others, demonstrate that deformation of partially molten rocks can lead to spontaneous localization into melt-rich networks that weaken the rock and provide efficient paths for heat and melt transport. Thus understanding the dynamics of partially molten systems is critical for understanding the behavior and evolution of plate boundaries. The aim of this project is to advance our theoretical understanding of the process, in order to extrapolate results from experiments to a wide range of conditions in the Earth. There exists a wealth of data from high-pressure and temperature experiments on partially molten rocks deformed in torsion, from which a great deal of information about the mechanisms active in stress-driven segregation may be inferred. The emphasis of this project is to develop better theoretical and computational models of these experiments. We are using two methods in parallel to model the process and compare model to experiment. The first is to develop numerical models of the partial differential equations derived from two-phase flow or magma dynamics theory, solved in torsional deformation geometry. A spinoff of this work will be the development and release of an advanced computational system for general multi-physics problems. The effects to be tested will include various constitutive models for matrix deformation as well as various effects of surface energy and damage. The second methodology is to develop effective macroscopic constitutive models within a non-equilibrium thermodynamic framework, using a formalism that is well-established in metallurgy but is just beginning to be applied to earth science. This method describes the structural characteristics of the material with "internal state variables", and tracks the stored and dissipated energy associated with those. The result will be thermodynamically consistent constitutive equations that can be solved in geodynamic models that explore the large-scale effects of stress-driven segregation occurring at length scales much smaller than can ever be resolved in a geodynamic model. This effective constitutive model will also include melt transport properties so that the potential consequences of coupling between deformation and fluid flow can be explored in subduction zones, ridges, rifts and other planetary settings.