Shock Wave Studies of Mineral and Melt Physics at Deep Mantle Pressures

对地球内部深处的研究对于了解我们星球的长期演变至关重要，包括我们居住的地表的可居住性和自然灾害。我们特别感兴趣的是深部内部的熔化，以及它对地幔化学演化的影响。然而，深海的极端条件，特别是高压和高温，以及在这种深度直接观测的局限性，要求应用专门的实验技术。一种技术使用大型固定枪以高速将矿物和金属目标碰撞在一起，从而在短时间内产生非常高的压力，这种方法被称为冲击波研究。我们可以用这些实验进行的测量是独特的，但也是对其他实验和理论技术所获得结果的补充。我们将致力于在未来三年内加州理工学院的冲击波实验室的熔融和下地幔条件下的矿物和熔体的热力学性质的研究。最终的目标是发展精确的相平衡模型和简化地幔成分的物理性质，可以与地球物理观测数据进行比较，或插入到今天可能发生在深部地幔的过程的动态模型中，例如地幔柱的形成，或可能发生在地球历史早期，例如岩浆海洋结晶。在地幔底部地震观测到的超低速带可能构成部分熔融区域的温度、成分和相对浮力的合理限制下，我们将限制这些区域存在的动力学和化学后果。同样，液相线矿物学以及液体和固体的相对浮力的知识有助于确定早期陆地全地幔岩浆海洋如何通过结晶分异演化，从而确定固体地幔演化的初始状态。我们的实验方法将是同时测定透明材料中的激波速度、声速和激波温度，主要是MgO和MgSiO3冲击进入下地幔相组合。所有这些量的确定一起提供了最佳的约束熔化曲线和固体和液体的状态参数的热方程。我们专注于地球物理感兴趣的材料，由于现有数据和实验能力的限制，这些数量仍然是最不确定的。我们已经证明，通过声速测量多孔氧化镁，我们能够冲击熔化这种材料，并确定其高度不确定的熔化曲线的位置。我们将继续使用不同的孔隙率和预热单晶这一计划，以获得更多的限制熔化曲线，并确定未知的热物理性质的MgO液体。我们现有的数据库中的MgSiO3系统的冲击结果，我们建议增加一系列的冲击速度，声速，冲击温度测量单晶顽火辉石和预热MgSiO3液体，以消除参数的权衡，在热力学描述这种液体组合物。

Study of the deep interior of the Earth is essential to understanding the long-term evolution of our planet, including the habitability and natural hazards of the surface where we live. We are particularly interested in the melting of the deep interior, and its consequences for the chemical evolution of the mantle. The extreme conditions that characterize great depth, particularly high pressure and temperature, and the limits of direct observations at such depths, however, require the application of specialized experimental techniques. One family of techniques uses large stationary guns to collide mineral and metal targets together at high speed and so generate very high pressures for a short time, a method referred to as shock wave research. The measurements that we can make with these experiments are unique, but also complementary to results obtained by other experimental and theoretical techniques. We will dedicate the Caltech shock wave laboratory over the next three years to the study of melting and the thermodynamic properties of minerals and melts under lower mantle conditions. The ultimate goal is development of accurate models of phase equilibria and physical properties of simplified mantle compositions that can be compared to geophysical observables or inserted into dynamic models of processes that may occur in the deep mantle today, such as formation of mantle plumes, or that may have occurred early in Earth history, such as magma ocean crystallization. With constraints on the plausible temperature, composition, and relative buoyancy of partially molten regions that might constitute the ultra-low velocity zones seismically observed at the base of the mantle, we will place limits on the dynamical and chemical consequences of the existence of such zones. Likewise, knowledge of the liquidus mineralogy and the relative buoyancy of liquids and solids helps to define how an early terrestrial whole-mantle magma ocean might have evolved by crystallization-differentiation and so the initial state of solid mantle evolution.Our experimental approach will be simultaneous determination of shock velocity, sound speed, and shock temperature in transparent materials, principally MgO and MgSiO3 shocked into lower mantle phase assemblages. Determination of all these quantities together provides optimal constraints on melting curves and thermal equation of state parameters of solids and liquids. We focus this effort on materials of geophysical interest where these quantities remain most uncertain due to limitations of existing data and experimental capabilities. We have demonstrated through sound-speed measurements on porous MgO that we are able to shock melt this material and define the location of its highly uncertain melting curve. We will continue this program using different porosities and pre-heated single crystals both to obtain more constraints on the melting curve and to define the unknown thermophysical properties of MgO liquid. To our existing database of shock results in the MgSiO3 system, we propose to add a series of shock velocity, sound speed, and shock temperature measurements on single crystal enstatite and on preheated MgSiO3 liquid in order to remove parameter trade-offs in the thermodynamic description of this liquid composition.