Collaborative Research: 3D Dynamics of Buoyant Diapirs in Subduction Zones

地球表面和内部之间的热量和化学物质的交换受到板块构造的控制。具体地说，地球？S板块在俯冲带被循环回到地幔，在那里一个构造板块被压在另一个板块之下。在俯冲过程中，下降板块中的一些物质返回到地表，形成了地球--S地壳。这种迁移很大程度上是通过俯冲物质的熔化和随后的地表火山作用进行的，然而，浮力物质也可以通过底辟中的固态流动返回地表。这个项目的目标是利用实验室实验和数值模型相结合的方法来研究这些浮力底辟的上升。我们将使用这些模型来确定底辟形成的地点和时间，并确定底辟特征(体积/浮力)与从下降板到地表的上升路径之间的关系。由于浮力底辟与直接从俯冲板块产生的熔体具有不同的化学特征，因此了解这一过程的效率对于确定地球的化学演化至关重要。该项目还将支持一名博士生和一名博士后研究员的教育。尽管之前的许多研究都研究了俯冲板块驱动的地幔流动，但相对较少的研究关注的是浮力物质从板块上升回到地表。在这个项目中，我们将描述底辟演化的3个阶段：形成阶段、上升阶段和到达阶段，并确定每个阶段是如何受到板块驱动的地幔楔形流场的影响的。实验室实验将被用来模拟三维上升底辟的路径和相互作用，作为板块驱动流场的特定方面的函数，包括板块回滚、板块几何形状的沿走向变化(例如，板块边缘、缝隙、倾角变化)和覆盖板块的变形。底辟将在假设不同浮力来源的情况下启动，包括点源、线源和下行板表面的浮力材料片。我们预计底辟上升路径将受到底辟体积(浮力)通量和地幔楔形中的流动模式的强烈影响-潜在地导致浮板衍生的物质向地表的巨大水平净输送。然后，将使用高分辨率数值模型，根据密度对比度、底辟大小、路径形状和穿越时间来研究上升底辟光谱内的熔融和熔融-基质相互作用。这类模型对于描述底辟内的化学分化很重要。结合实验室实验和数值模型，我们将能够对化学信号如何从板块传输到俯冲区的表面施加重要的新限制。

The exchange of heat and chemical species between the surface and interior of the Earth are controlled by plate tectonics. Specifically, the Earth?s plates are recycled back into the mantle at subduction zones, where one tectonic plate is forced beneath another. During subduction some of the material from the descending plate is returned to surface forming the Earth?s crust. Much of this transport occurs via melting of the subducted material and subsequent volcanism at the surface, however, buoyant material can also return to the surface via solid-state flow in ?diapirs?. The goal of this project is to study the rise of these buoyant diapirs using a combination of laboratory experiments and numerical models. We will use these models to ascertain where and when diapirs form and to determine the relationship between diapir characteristics (volume/buoyancy) and ascent paths from the descending slab to the surface. Because buoyant diapirs will have different chemical signatures than the melts generated directly from the subducting plate, understanding the efficiency of this process is critical for determining chemical evolution of the Earth. This project will also support the education of a PhD student and a post-doctoral research fellow.While many previous studies have investigated mantle flow driven by the subducting slab, relatively few have focused on the ascent of buoyant material from the slab back to the surface. In this project we will characterize the 3 stages of diapir evolution: formation stage, rise stage, and arrival stage, and determine how each is influenced by the plate-driven mantle wedge flow field. The laboratory experiments will be used to model the pathways and interaction of ascending diapirs in three dimensions as a function of specific aspects of the plate-driven flow field, including slab rollback, along-strike variations in slab geometry (e.g., slab edges, gaps, changes in dip), and deformation of the overriding plate. Diapirs will be initiated assuming different buoyancy sources including a point source, line source, and sheet of buoyant material on the surface of the down-going slab. We expect that diapir ascent paths will be strongly influenced by diapir volume (buoyancy) flux and the pattern of flow in the mantle wedge?potentially resulting in large horizontal net transport of buoyant slab-derived material to the surface. High-resolution numerical models will then be used to study melting and melt-matrix interaction within the spectrum of ascending diapirs based upon density contrast, diapir size, path shape and transit time. Such models are important for characterizing chemical differentiation within diapirs. Combining the laboratory experiments with the numerical models, we will be able to place important new constraints on how chemical signals can be transported from the slab to the surface in subduction zones.