Collaborative Research: Apatite petrochronology and microtextural analyses: a new tool to directly date subduction processes at the base of the seismogenic zone

合作研究：磷灰石岩石年代学和微观结构分析：直接测定地震带底部俯冲过程的新工具

• 批准号: 2217811
• 负责人: Cailey Condit
• 金额: $ 25.32万
• 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: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2025-11-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2217811&HistoricalAwards=false
• 关键词: Collaborative; Research; Apatite; petrochronology; microtextural

Subduction zones are the locus for the most destructive geological hazards on earth including megathrust earthquakes, volcanic eruptions, and tsunami. The portion of the subduction zone where large earthquakes nucleate and slow earthquakes occur, known as the base of the seismogenic zone, is also an area where intense chemical change and fluid flow occurs. Understanding the timing and processes associated with these rocks deformating and interacting with fluids in this part of the subduction zone is critical for further constraining these earthquakes and global element cycling. However, we currently lack robust tools to do so. This project aims to develop apatite petrochronology, the integration of chronologic, chemical, and textural data from single grains of the common mineral apatite, to directly date chemical and mechanical processes that occurred at the base of the subduction seismogenic zone. The proposed research will provide new tools for researchers studying subduction zones as well as deformation and fluid-rock interactions more broadly. The broader impacts of this work center around providing education and research opportunities that increase inclusivity and accessibility in geoscience through the development of virtual field video game modules that integrate field and lab observations and with petrologic, microstructural, and chronological results from this research. These video games will give students opportunities to gain field skills and link outcrop to microscale observations, while being inclusive and accessible to all students (i.e., no barriers associated with cost or able-bodiedness). This research supports two early career female scientists, a female postdoctoral researcher, and will support an undergraduate and graduate student at UNLV. The base of the subduction seismogenic zone, which occurs at depths of 30-50 kms and temperatures ~200-500°C, is where both large megathrust earthquakes nucleate and enigmatic fault zone behaviors such as episodic tremor and slip occur. This is also an area of intense chemical transformation including devolatilization, fluid flow, and metamorphism. Chemical, mechanical, and fluid processes occurring along the plate interface likely play an important role in influencing the deformation style of the base of the subduction seismogenic zone within the relatively cool greenschist and blueschist metamorphic facies (250°C - 500°C). We currently lack well constrained in situ chronometers in these relatively cold metamorphic rocks, making it challenging to place direct timing constraints on these chemical and mechanical processes in exhumed subduction complexes. Apatite, a common accessory mineral in many subduction zone lithologies, dynamically recrystallizes during deformation, dissolves and reprecipitates during fluid flow, and chemically tracks metamorphic and metasomatic reactions making it a potentially transformative tool for recovering linked microstructure-metamorphism-Temperature-time data. This project tests the hypothesis that apatite U-Pb petrochronology can directly date deformation, metamorphism, and(or) fluid flow in rocks exhumed from the base of the subduction seismogenic zone. Through coupled microstructural (petrographic, EBSD), geochemical (EPMA, LA-ICP-MS), and geochronological (LA-ICP-MS) techniques the researchers will directly date these processes in four exhumed subduction complexes (C. Alps, Catalina Schist, & Crete/Andros, Greece) representing different stages of the subduction evolution across a range of P-T-fluid conditions and lithologies. Their results will systematically constrain the physical and chemical behavior of apatite across different P-T and fluid conditions and facilitate method development of EPMA mapping of apatite, yielding transformative tools for recovering linked microstructure-T-t data. Ultimately, this will provide rheologic, geochronologic, and geochemical constraints on from exhumed subduction related rocks that can be integrated with remote observations (e.g., seismology, geodetic data) to better understand complexities of subduction earthquakes, creeping deformation, slow slip events, and chemical transformations during metamorphism, metasomatism, and fluid flow.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.

俯冲带是地球上最具破坏性的地质灾害的发源地，包括巨型逆冲地震、火山喷发和海啸。俯冲带中大地震孕育和缓慢地震发生的部分，被称为孕震带的底部，也是发生强烈化学变化和流体流动的区域。了解这些岩石在俯冲带这一部分变形并与流体相互作用的时间和过程，对于进一步限制这些地震和全球元素循环至关重要。然而，我们目前缺乏强大的工具来做到这一点。该项目旨在开发磷灰石岩石年代学，将来自普通矿物磷灰石单颗粒的年代学、化学和结构数据整合在一起，以直接测定俯冲地震孕育区底部发生的化学和机械过程。这项拟议的研究将为研究人员更广泛地研究俯冲带以及变形和流体-岩石相互作用提供新的工具。这项工作的更广泛影响集中在提供教育和研究机会，通过开发虚拟野外视频游戏模块，将野外和实验室观察与岩石学、微结构和年代学结果相结合，增加地球科学的包容性和可及性。这些视频游戏将使学生有机会获得实地技能，并将露头与微观观测联系起来，同时具有包容性和所有学生都能获得的机会(即，没有与成本或健全相关的障碍)。这项研究支持两名职业生涯早期的女科学家，一名女性博士后研究员，并将支持UNLV的一名本科生和研究生。俯冲地震孕育带的底部是大型逆冲地震的孕育区，深度30-50公里，温度约200-500°C，既是大型逆冲地震的孕育区，又是幕式地震、滑动等神秘断裂带活动的发源地。这也是一个强烈的化学转化区域，包括脱挥发、流体流动和变质作用。在相对较冷的绿片岩和蓝片岩变质相(250°C-500°C)中，沿板块界面发生的化学、力学和流体作用可能对俯冲孕震带底部的变形方式起到重要作用。目前，我们在这些相对较冷的变质岩中缺乏良好的原位计时，这使得在折返的俯冲杂岩中对这些化学和机械过程施加直接的时间限制是具有挑战性的。磷灰石是许多俯冲带岩性中常见的副矿物，在变形过程中动态重结晶，在流体流动过程中溶解和再沉淀，并在化学上跟踪变质和交代反应，使其成为恢复微结构-变质-温度-时间数据的潜在转换工具。该项目验证了磷灰石U-Pb岩石年代学可以直接测定俯冲地震带底部岩石中的变形、变质和(或)流体流动的假设。通过显微构造(岩石学，EBSD)、地球化学(EPMA，LA-ICPMS)和地质年代学(LA-ICPMS)的耦合技术，研究人员将在四个出土的俯冲杂岩(C.Alps，Catalina Sist，&Amp；Crete/Andres，希腊)中直接测定这些过程的时间，这些俯冲杂岩代表了一系列P-T流体条件和岩性的俯冲演化的不同阶段。他们的结果将系统地约束磷灰石在不同P-T和流体条件下的物理和化学行为，并促进磷灰石EPMA图谱的方法开发，产生用于恢复关联的微结构-T-t数据的变革性工具。最终，这将为挖掘出的俯冲相关岩石提供流变学、地质年代学和地球化学方面的约束，这些岩石可以与远程观测(例如地震学、大地测量数据)相结合，以更好地了解俯冲地震、蠕动变形、慢滑事件以及变质、交代和流体流动期间化学变化的复杂性。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。