Collaborative Research: Constraining the thermal conditions of the subduction interface by integrating petrology and geodynamics

合作研究：通过整合岩石学和地球动力学来约束俯冲界面的热条件

• 批准号: 1850713
• 负责人: Besim Dragovic
• 金额: $ 9.93万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-04-01 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1850713&HistoricalAwards=false
• 关键词: Collaborative; Research; Constraining; thermal; conditions

Subduction zones are places on Earth where one of Earth's tectonic plates dives beneath another. They are the location of many societally-relevant hazards, including the generation of Earth's deadliest earthquakes, such as the 2011 Tohoku earthquake and associated tsunami, and volcanic eruptions such as those at Mt St Helens (1980) and Mt Pinatubo (1991). The processes that lead to these earthquakes and volcanoes are ultimately dependent on the thermal structure of subduction zones - that is how hot it is at great depths. Metamorphic rocks exhumed from ancient subduction zones contain unique records of the temperatures that they witnessed as they traveled down a subduction zone before being exhumed. Geodynamic models and geophysical observations provide estimates of the thermal structures of present-day subduction zones. Interestingly, the rock record suggests significantly warmer conditions than those predicted for modern subduction zones. The proposed work will investigate the reasons for this discrepancy, which may lie in the way we interpret conditions from the rocks, the way they are exhumed, or even in how we compare model predictions and the rock record.This proposal aims to address the rock-model discrepancy through two key questions: 1) Does our current interpretation of the rock record accurately represent the thermal structure of the associated ancient subduction zone? and 2) Did rocks get exhumed from ancient subduction zones that were hotter on average than modern subduction zones? To address Question 1 this team will determine P-T conditions for metamorphic rocks exhumed from five well-characterized localities that represent a range of thermal structures using relatively new analytical methods: trace element thermometers (e.g. Zr-in-rutile) and mineral inclusion barometers (e.g. quartz-in-garnet barometry). To address Question 2, they will develop geodynamical models of the ancient subduction zones represented by the exhumed rocks. These models will incorporate the effects of region-specific subduction dynamics, such as variations in slab age and subduction rate with time, subduction initiation, ridge subduction, and slab breakoff, when applicable. The model-predicted P-T conditions along the subduction interface will be compared with the newly produced P-T estimates to re-evaluate their disparity. The two-pronged approach of combining petrological observations and geodynamical modeling allows quantitative exploration of the thermal evolution of subduction zones. Subduction-related metamorphic rocks are the only direct samples of material from the plate interface; evaluating the P-T conditions using the latest thermobarometric approaches will provide the team with a more accurate and precise way to untangle the complex history they have experienced. Through geodynamical modeling, the effects of individual parameters on the thermal structure of subduction zones can be isolated, and this targeted approach will allow evaluation of possible explanations for the warm conditions that are recorded by exhumed rocks. The application of the two-pronged approach to the selected ancient subduction localities will allow researchers to determine whether the disparity can be reconciled. The results of this work have important implications for many processes, including geochemical cycling of volatiles, construction of continental crust, and the conditions that lead to arc volcanism. This work will engage graduate students and early career scientists in new collaborations between scientists of different disciplines (petrologists and geodynamicists) and at different institutions both in the US and abroad. EarthCache (TM) sites will be created in California (Franciscan and Catalina) as part of the project. These sites will engage the public in geoscience through the popular activity of geocaching and will disseminate information about subduction zone geology through information tied to direct observations of geologic features exhumed from subduction zones.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.

俯冲带是地球上的一个构造板块俯冲到另一个构造板块之下的地方。它们是许多与社会有关的危险的所在地，包括地球上最致命的地震的产生，如2011年东北地震和相关的海啸，以及圣海伦山（1980年）和皮纳图博山（1991年）的火山爆发。导致这些地震和火山爆发的过程最终取决于俯冲带的热结构--也就是说，它在很深的地方有多热。从古代俯冲带中挖掘出来的变质岩包含了独特的温度记录，这些记录是他们在被挖掘出来之前沿着俯冲带旅行时所目睹的。地球动力学模型和地球物理观测提供了对现今俯冲带热结构的估计。有趣的是，岩石记录表明，比现代俯冲带预测的温度要高得多。这项工作将调查这种差异的原因，这可能在于我们解释岩石条件的方式，它们被挖掘的方式，甚至是我们如何比较模型预测和岩石记录。这项建议旨在通过两个关键问题来解决岩石模型的差异：1）我们目前对岩石记录的解释是否准确地代表了相关的古代俯冲带的热结构？2）岩石是否是从平均温度高于现代俯冲带的古代俯冲带中挖掘出来的？为了解决问题1，该团队将使用相对较新的分析方法确定从五个特征良好的地方挖掘出的变质岩的P-T条件，这些地方代表了一系列热结构：微量元素温度计（例如金红石中的Zr）和矿物包裹体气压计（例如石榴石中的石英气压计）。为了解决第二个问题，他们将开发出以出土岩石为代表的古代俯冲带的地球动力学模型。这些模型将纳入特定区域俯冲动力学的影响，如板片年龄和俯冲速率随时间的变化、俯冲起始、脊俯冲和板片断裂（如适用）。模型预测的P-T条件沿着俯冲界面将与新产生的P-T估计值进行比较，以重新评估其差异。岩石学观测和地球动力学模拟相结合的双管齐下的方法允许定量探索俯冲带的热演化。与俯冲有关的变质岩是来自板块界面的唯一直接材料样本;使用最新的温压法评估P-T条件将为团队提供一种更准确和精确的方法来解开他们所经历的复杂历史。通过地球动力学建模，可以分离出各个参数对俯冲带热结构的影响，这种有针对性的方法将有助于评估对挖掘岩石记录的温暖条件的可能解释。将双管齐下的方法应用于选定的古代俯冲地点将使研究人员能够确定这种差异是否可以调和。这项工作的结果对许多过程具有重要意义，包括挥发物的地球化学循环，大陆地壳的构造以及导致弧火山作用的条件。这项工作将使研究生和早期职业科学家参与不同学科（岩石学家和地球动力学家）和美国国内外不同机构的科学家之间的新合作。作为该项目的一部分，将在加州（方济各会和卡塔利纳）建立地球缓存（TM）网站。这些地点将通过地质寻宝的大众活动吸引公众参与地球科学，并将通过直接观察从俯冲带挖掘出的地质特征来传播有关俯冲带地质的信息。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。