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Collaborative Research: Probing feedbacks between thermal structure, petrologic transformation, and rheologic evolution within dynamically evolving subduction zones

合作研究：探测动态演化俯冲带内的热结构、岩石学转变和流变演化之间的反馈

基本信息

批准号：
2119844
负责人：
Cailey Condit
金额：
$ 18.66万
依托单位：
University of Washington
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2021
资助国家：
美国
起止时间：
2021-08-01 至 2024-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2119844&HistoricalAwards=false
关键词：
Collaborative Research Probing feedbacks between

项目摘要

Subduction zones – places where one tectonic plate sinks beneath another – are responsible for the generation of deadly earthquakes, explosive volcanoes, global chemical cycling into the deep earth, and tectonic plate movements. The thermal structure of a subduction zone (i.e., the temperature of different parts of the subduction zone at depth) exerts a first order control on the strength and mechanics of an individual subduction zone and also on what materials and volatiles (e.g., water) are transported down to the deep earth within subducting plates. Together, these temperature-dependent mechanical and chemical processes dictate the occurrence of subduction zone hazards such as earthquakes and volcanism. Thus, a longstanding goal of subduction research is a quantitative understanding of subduction zone thermal structure. Because these zones are 100s of km thick and 1000s of km long, we cannot directly measure their thermal structure. However, we can create detailed numerical simulations (subduction models) that predict thermal structure and allow us to investigate how it evolves and influences these mechanical and chemical processes. These models are guided by a broad range of tectonic observables in active subduction zones and by studies of subducted rocks that have been exhumed back to the surface. These data illuminate a range of thermal, chemical (petrological), and mechanical (rheological) feedbacks that operate over the lifetime of a subduction zone but are typically omitted from thermal subduction zone models. For instance, chemical reactions (e.g., metamorphism) in subducting plates are not only highly-temperature dependent, but also likely to affect the thermal structure of subduction zones. This is because different metamorphic rocks have different strengths and densities which, in turn, affect the subduction properties (convergence velocity between the two plates, dip angle of the subducting plate) that ultimately control subduction zone temperature. Motivated by these dynamic interactions, we will develop a suite of subduction models that directly incorporate these thermal-chemical-mechanical feedbacks. This modeling approach will allow us to probe how, and how rapidly, subduction zone thermal structure evolves, and also to characterize how this thermal variability impacts plate boundary strength and chemical cycling in these important tectonic zones. In addition to supporting undergraduate, graduate, and postdoctoral researchers, this project will also benefit society and the geoscience community through a combination of education, outreach, and scientific in-reach in the following ways: (1) we will develop an online lab activity for introductory geology classes to expose beginning geoscientists to computational methods, (2) we will host an in-reach subduction zone workshop at the University of Washington, and (3) we will reach out to the public by developing a digital exhibit on subduction zones at The Beneski Museum of Natural History (Amherst College).To capture dynamic and time-evolving subduction behavior for Earth’s range of subduction settings, we will fully integrate geodynamic, petrologic, and rheological components into our modeling framework. Petrologic modeling will reveal the loci of slab devolatilization and density transformations through time. A suite of experimentally and geologically constrained rheologies will be used to calculate the time-evolving crustal viscosity structure. Both components will be fully integrated into the geodynamic modeling component (i.e., a time-dependent subduction model) so that calculated petrological phases, densities, and viscosities are dictated by, and also affect, the thermal evolution of the geodynamic model. After iteratively increasing the complexity of models (so as to preserve physical intuition as the number of model components grow), we will run models for parameter combinations corresponding to each subduction system on Earth. This will enable us place bounds on the properties of Earth’s slabs (temperature, dehydration systematics, density, viscosity), in space and time, and address three targeted questions relating to the co-evolution of slab thermal structure, dehydration, and mechanical properties: What evolutionary phase of subduction is associated with the most water transport to the deep mantle? What is the mechanical control on the so-called “decoupling depth” at subduction zones? And, lastly, what is the dominant control on the bi-modal timing of subducted rock exhumation?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

俯冲带——一个构造板块下沉到另一个板块下面的地方——是造成致命地震、火山爆发、全球化学循环进入地球深处以及构造板块运动的原因。俯冲带的热结构（即俯冲带深处不同部分的温度）对单个俯冲带的强度和力学，以及在俯冲板块内哪些物质和挥发物（如水）被输送到地球深处起着一级控制作用。这些与温度有关的机械和化学过程共同决定了诸如地震和火山活动等俯冲带危险的发生。因此，对俯冲带热结构的定量认识是俯冲研究的一个长期目标。因为这些区域有100公里厚，1000公里长，我们不能直接测量它们的热结构。然而，我们可以创建详细的数值模拟（俯冲模型）来预测热结构，并允许我们研究它是如何演变和影响这些机械和化学过程的。这些模型的指导依据是在活动俯冲带中广泛的构造观测结果，以及对被挖出地表的俯冲岩石的研究。这些数据阐明了一系列的热、化学（岩石学）和力学（流变学）反馈，这些反馈贯穿于俯冲带的整个生命周期，但通常在热俯冲带模型中被忽略。例如，俯冲板块中的化学反应（如变质作用）不仅依赖于高温，而且可能影响俯冲带的热结构。这是因为不同的变质岩具有不同的强度和密度，这反过来又影响了最终控制俯冲带温度的俯冲性质（两个板块之间的收敛速度，俯冲板块的倾角）。在这些动态相互作用的激励下，我们将开发一套直接结合这些热-化学-机械反馈的俯冲模型。这种建模方法将使我们能够探索俯冲带热结构的演变方式和速度，并描述这种热变化如何影响这些重要构造带的板块边界强度和化学循环。除了支持本科生、研究生和博士后研究人员外，该项目还将通过以下方式，通过教育、推广和科学深入相结合，造福社会和地球科学界：(1)我们将为地质学入门课程开发一个在线实验室活动，让初级地球科学家接触到计算方法；(2)我们将在华盛顿大学举办一个可触及的俯冲带研讨会；(3)我们将通过在贝内斯基自然历史博物馆（阿默斯特学院）开发一个关于俯冲带的数字展览来接触公众。为了捕捉地球俯冲环境范围内的动态和随时间变化的俯冲行为，我们将把地球动力学、岩石学和流变学成分完全整合到我们的建模框架中。岩石学建模将揭示板岩脱挥发和密度随时间变化的轨迹。一套实验和地质约束流变学将用于计算随时间变化的地壳粘度结构。这两个部分都将被完全整合到地球动力学建模组件中（即，一个随时间变化的俯冲模型），这样计算出来的岩石相、密度和粘度就会受到地球动力学模型的热演化的影响。在迭代地增加模型的复杂性（以便在模型组件数量增长时保持物理直觉）之后，我们将运行模型，以对应地球上每个俯冲系统的参数组合。这将使我们能够确定地球板块的属性（温度、脱水系统、密度、粘度）在空间和时间上的界限，并解决与板块热结构、脱水和力学特性共同演化有关的三个有针对性的问题：俯冲的哪个演化阶段与向深部地幔输送最多的水有关？对俯冲带所谓“解耦深度”的机械控制是什么？最后，对俯冲岩石发掘双模态时间的主要控制因素是什么？该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。