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

合作研究：俯冲带浮力底辟的 3D 动力学

• 批准号: 1316333
• 负责人: Mark Behn
• 金额: $ 24万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-01 至 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1316333&HistoricalAwards=false
• 关键词: Collaborative; Research; 3D; Dynamics; Buoyant

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.

地球表面和内部之间的热量和化学物质的交换受板块构造的控制。 具体来说，地球？在俯冲带，一个构造板块被压在另一个构造板块之下。 在俯冲过程中，一些来自下降板块的物质返回到形成地球的表面？的外壳。 这种运输大部分发生通过融化的俯冲物质和随后的火山活动在表面，但是，浮力材料也可以返回到表面通过固态流？底辟？ 该项目的目标是研究这些浮力底辟的上升，使用实验室实验和数值模型相结合。 我们将使用这些模型来确定底辟形成的时间和地点，并确定底辟特征（体积/浮力）和从下降板到表面的上升路径之间的关系。 由于浮力底辟与俯冲板块直接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。 该项目还将资助一名博士生和一名博士后研究员的教育。虽然以前有许多研究调查了俯冲板片驱动的地幔流动，但相对较少的研究集中在浮力物质从板片升回地表。 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，到达阶段，并确定每个阶段是如何受到板块驱动的地幔楔流场的影响。 实验室实验将用于模拟三维上升底辟的路径和相互作用，作为板块驱动流场特定方面的函数，包括板块回滚、板块几何形状的沿走向变化（例如，板边缘、间隙、倾角变化）和上覆板块的变形。 假设不同的浮力源（包括点源、线源和下行板表面上的浮力材料片）将引发底辟。 我们预计，底辟上升路径将强烈影响底辟体积（浮力）通量和地幔楔中的流动模式？潜在地导致浮板衍生材料向表面的大的水平净输送。 高分辨率的数值模型，然后将被用来研究熔融和熔融基质的相互作用的频谱内的上升底辟的基础上密度对比，底辟的大小，路径形状和过境时间。 这些模型对于描述底辟内部的化学分异作用是很重要的。 将实验室实验与数值模型相结合，我们将能够对化学信号如何从俯冲带中的板片传输到表面施加重要的新约束。