Testing contrasting models for the distribution of hydrothermal circulation in subducting crust

俯冲带是地球上的一个板块在另一个板块下移动的地方，导致了世界上许多最大的地震和破坏性的海啸。其中一个例子是2011年日本北部发生的地震和海啸，造成2万多人死亡，福岛第一核电站（Fukushima Daiichi）受损。这些地震是由分隔两个构造板块的俯冲带断层的摩擦引起的。俯冲断裂带的温度影响这种摩擦，并能控制地震的大小和分布。此外，俯冲带的温度还影响着其他广泛的物理和化学过程，包括为附近火山提供补给的岩浆的产生。为了了解这些过程，准确估计俯冲带的温度是很重要的。最近的发现表明，俯冲构造板块内的海水循环是控制俯冲带温度的重要因素。该项目将研究当构造板块向下弯曲进入俯冲带时，在板块上部打开的裂缝如何影响系统中的海水循环，以及这如何影响俯冲带的温度。该项目将开发7个俯冲带的数值热模型。这项研究结果的应用具有直接的社会效益，可以为地震危害评估提供信息。此外，该项目将加强新墨西哥理工大学的教育，这是一所专注于stem的西班牙裔服务机构。研究生将接受地球物理学和水文地质学方面的培训。该项目的成果将纳入“在课堂上使用数据”的努力，提高本科课程的实践经验。准确的俯冲带热模型对于了解俯冲板的摩擦行为、变质反应过程、挥发物的释放、地幔楔水化作用、俯冲动力学和熔体的产生是必要的。海洋地壳含水层的流体循环是俯冲带温度的重要控制因素。然而，对于有多少海洋地壳可以容纳剧烈的热液循环，有不同的假设。板块弯曲正断层导致的海洋地壳含水层增厚以及俯冲地壳与海沟向海地壳之间的流体循环都可能导致热量的平流再分布，从而影响俯冲带的温度。该项目将验证一个假设，即在俯冲前含水层增厚对曲率较大的板块的热效应更大。本项目将利用从外凸起到海沟的含水层增厚和俯冲地壳中持续的流体循环预计会产生明显的地表热通量异常（含水层增厚为宽的低振幅异常；俯冲地壳中流体循环为窄的高振幅异常），以约束每个过程的热效应。这将促进我们对流体循环过程的理解，流体循环过程是俯冲带温度的重要控制因素，并改进本项目和其他项目中研究的七个边缘的俯冲带热模型。

Subduction zones are where one of Earth's tectonic plates moves under another resulting in many of the world's largest earthquakes and damaging tsunamis. One example is the 2011 earthquake and tsunami in northern Japan that killed more than 20,000 people and crippled the Fukushima Daiichi nuclear complex. These earthquakes arise from friction on the subduction zone fault that separates the two tectonic plates. The temperature of the subduction fault zone affects this friction and can control the size and distribution of earthquakes. In addition, subduction zone temperatures affect a wide range of other physical and chemical processes, including the generation of magma that supplies nearby volcanoes. To understand these processes, it is important to accurately estimate subduction zone temperatures. Recent discoveries show that seawater circulating within the subducting tectonic plates is an important control on subduction zone temperatures. This project will examine how fractures that open in the upper part of a tectonic plate as it bends down into a subduction zone affect seawater circulation in the system and how that affects subduction zone temperatures. The project will develop numerical thermal models for seven subduction zones. Application of the results of this research has direct societal benefit, by informing earthquake hazard estimates. In addition, the project will enhance education at New Mexico Tech, a STEM-focused Hispanic-serving institution. A graduate student will be trained in geophysics and hydrogeology. Results of the project will be incorporated into "using data in the classroom" efforts, improving hands-on experience in undergraduate courses.Accurate subduction zone thermal models are necessary to understand frictional behavior, metamorphic reaction progress, release of volatiles from the subducting slab, mantle wedge hydration, subduction dynamics, and melt generation. Fluid circulation in an oceanic crustal aquifer is an important control on subduction zone temperatures. However, there are contrasting hypotheses for how much of the oceanic crust can host vigorous hydrothermal circulation. Both thickening of the oceanic crustal aquifer via plate bending normal faults and fluid circulation between subducted crust and the crust seaward of the trench may contribute to the advective redistribution of heat that affects subduction zone temperatures. This project will test the hypothesis that the thermal effects of aquifer thickening prior to subduction are greater for slabs with a greater degree of curvature. This project will exploit the fact that aquifer thickening from the outer rise to the trench and continued fluid circulation in subducting crust are expected to produce distinct surface heat flux anomalies (a broad low amplitude anomaly for aquifer thickening; a narrow high amplitude anomaly for fluid circulation in subducting crust) in order to constrain the thermal effects of each process. This will advance our understanding of the fluid circulation process that is an important control on subduction zone temperatures, improving subduction zone thermal models for the seven margins examined in this project and others.