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：
2119842
负责人：
Adam Holt
金额：
$ 28.78万
依托单位：
University of Miami
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=2119842&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（一个构造板块沉入另一个构造板块的地方）是造成致命地震、火山爆发、进入地球深处的全球化学循环以及构造板块运动的原因。俯冲带深度的不同部分）对单个俯冲带的强度和力学以及哪些物质和挥发物（例如水）向下输送到地球深处施加一级控制这些与温度相关的机械和化学过程共同决定了俯冲带灾害（例如地震和火山活动）的发生，因此，俯冲带研究的长期目标是定量了解俯冲带的热结构。公里厚和数千公里长，我们无法直接测量它们的热结构，但是，我们可以创建详细的数值模拟（俯冲模型）来预测热结构，并允许我们研究它如何演化和影响这些机械和结构。这些模型以活跃俯冲带的广泛构造观测和对已挖掘回地表的俯冲岩石的研究为指导，这些数据阐明了一系列热、化学（岩石学）和机械（流变学）。）在俯冲带的整个生命周期内运行的反馈，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（例如变质作用）不仅是高温反应。相关，但也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，进而影响俯冲特性（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推动下，我们将最终控制俯冲带温度，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究俯冲带热的方式和速度。结构的演化，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造福社会和地球科学界。通过以下方式开展教育、推广和科学深入活动：(1) 我们将为入门地质学课程开发在线实验室活动，让初级地球科学家接触计算方法，(2) 我们将在大学华盛顿，(3) 我们将通过在贝内斯基自然历史博物馆（阿默斯特学院）开发俯冲带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演变的俯冲行为，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。岩石学建模将使用一套实验和地质约束的流变学来揭示板片脱挥发分和密度变化的轨迹。计算时间地壳粘度结构。这两个组件将完全集成到地球动力学建模组件（即依赖时间的俯冲模型）中，以便计算出的岩石相、密度和粘度由热力决定，并且也会影响热力。在迭代地增加模型的复杂性之后（以便随着模型组件数量的增长保留物理直觉），我们将运行与每个俯冲系统相对应的参数组合的模型。这将使我们能够在空间和时间上对地球板块的特性（温度、脱水系统、密度、粘度）进行限制，并解决与板块热结构、脱水和力学共同演化相关的三个有针对性的问题。性质：俯冲的哪个演化阶段与向地幔深处输送最多的水有关？对俯冲带所谓“脱钩深度”的机械控制是什么？俯冲岩石折返的双峰时间？该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。