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

• 批准号: 2119843
• 负责人: Victor Guevara
• 金额: $ 10.6万
• 依托单位: Amherst College
• 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=2119843&HistoricalAwards=false
• 关键词: Collaborative; Research; Probing; feedbacks; between

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（一个构造板下沉在另一个下面的地方）是导致致命的地震，爆炸性火山，全球化学循环到深层地球以及构造板块运动的原因。俯冲带的热结构（即俯冲带的不同部分在深度处的温度）对单个俯冲带的强度和力学以及在俯冲板内的材料和挥发物（例如水（例如，水）（例如，水）（例如，水）（例如，水）（例如，水）对俯冲板内的深层接收到一阶控制。总之，这些依赖温度的机械和化学过程决定了俯冲带危害（例如地震和火山）的发生。这是俯冲研究的一个长期目标是对俯冲带热结构的定量理解。由于这些区域是100 km厚的100 km和1000 km长，因此我们无法直接测量其热结构。但是，我们可以创建详细的数值模拟（俯冲模型），以预测热结构，并允许我们研究它如何发展并影响这些机械和化学过程。这些模型由活跃俯冲带中的各种构造观察者以及对已挖回表面的俯冲岩石的研究进行了指导。这些数据阐明了一系列热，化学（岩石学）和机械（流变）反馈，这些反馈在俯冲带的一生中运行，但通常从热俯冲带模型中省略。例如，俯冲板中的化学反应（例如变质）不仅是高温依赖性的，而且很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（两个板之间的收敛速度，俯冲板的倾斜角）最终控制俯冲区温度。由这些动态相互作用的动机，我们将开发一套俯冲模型，这些模型直接结合了这些热化学机械反馈。这种建模方法将使我们能够探索如何以及如何快速，俯冲带热结构的演变，并表征这种热变异性如何影响板边界强度和这些重要的构造区域的化学循环。 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 introduction geologic 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公众通过在贝内斯基自然历史博物馆（阿默斯特学院）开发一场关于俯冲区的数字展览，以捕获地球俯冲环境范围的动态和随时间变化的俯冲行为，我们将充分整合地球动力学，petrologic and Petrolologic和Rheogologications and Rheological Comptents and Rheological Comptents。岩石学建模将揭示板块devolatilization和密度转化的局部时间。一套实验和地质限制的流变套件将用于计算随着时间的发展的地壳粘度结构。这两个组件都将完全集成到地球动力学建模成分（即，时间依赖性的俯冲模型）中，以便计算出计算的岩石学相，密度和粘度由地球动力学模型的热演化决定。在迭代地增加了模型的复杂性（以将物理直觉保留为模型组件的增长次数）之后，我们将运行与地球上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占据地球平板（温度，脱水系统，密度，粘度）的特性，并解决与平板热结构，脱水和机械性能的共同进化有关的三个目标问题：俯冲的进化相位与大多数水的进化相关与深层的水层相关联？俯冲带上所谓的“解耦深度”的机械控制是什么？最后，对俯冲岩石挖掘的双模式时机的主要控制权是什么？该奖项反映了NSF的法定任务，并使用基金会的知识分子优点和更广泛的影响审查标准通过评估被认为是珍贵的支持。

项目成果

The effects of plate interface rheology on subduction kinematics and dynamics

板块界面流变学对俯冲运动学和动力学的影响

• DOI: 10.1093/gji/ggac075
• 发表时间: 2022
• 期刊: Geophysical Journal International
• 影响因子: 2.8
• 作者: Behr, Whitney M;Holt, Adam F;Becker, Thorsten W;Faccenna, Claudio
• 通讯作者: Faccenna, Claudio