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: 2217810
• 负责人: Margaret Odlum
• 金额: $ 37.02万
• 依托单位: University of Nevada Las Vegas
• 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 2023-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2217810&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生地，包括大型逆冲断层地震、火山爆发和海啸。俯冲带中大地震成核和慢地震发生的部分，被称为孕震带的基底，也是发生强烈化学变化和流体流动的区域。了解与这些岩石变形和与俯冲带这一部分流体相互作用相关的时间和过程，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，整合普通矿物磷灰石的单颗粒的年代学，化学和结构数据，以直接确定俯冲孕震带底部发生的化学和机械过程。这项研究将为研究俯冲带以及更广泛的变形和流体-岩石相互作用的研究人员提供新的工具。这项工作的更广泛的影响围绕提供教育和研究机会，通过开发虚拟现场视频游戏模块，将现场和实验室观察与岩石学，显微结构和年代学结果结合起来，提高地球科学的包容性和可访问性。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，所有学生都可以使用（即，没有与费用或身体健全有关的障碍）。这项研究支持两名早期职业女性科学家，一名女性博士后研究员，并将支持UNLV的本科生和研究生。俯冲孕震带的底部位于30-50公里深处，温度约为200-500°C，是大型逆冲断层地震成核和神秘断层带行为（如幕式震颤和滑动）发生的地方。这也是一个强烈的化学变化，包括脱挥发分，流体流动和变质作用的领域。沿着板块界面发生的化学、机械和流体过程可能在影响相对较冷的绿片岩和蓝片岩变质相（250°C - 500°C）内俯冲孕震带基底的变形方式方面发挥重要作用。我们目前缺乏很好的约束，在这些相对寒冷的变质岩原位计时器，使其具有挑战性的地方，这些化学和机械过程中的折返俯冲复合体的直接时间限制。 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，并以化学方式跟踪变质和交代反应，使其成为恢复相关显微结构-变质-温度-时间数据的潜在变革工具。该项目检验了磷灰石U-Pb岩石年代学可以直接测定从俯冲孕震带底部挖出的岩石中的变形、变质和（或）流体流动的假设。通过耦合显微结构（岩相学，EBSD），地球化学（EPMA，LA-ICP-MS）和地质年代学（LA-ICP-MS）技术，研究人员将直接确定四个折返俯冲复合体（C。阿尔卑斯山，卡塔利纳片岩，克里特岛/安德罗斯，希腊）代表了俯冲演化的不同阶段，跨越了一系列的P-T流体条件和岩性。他们的研究结果将系统地限制磷灰石在不同P-T和流体条件下的物理和化学行为，并促进磷灰石EPMA绘图的方法开发，为恢复相关的显微结构-T-t数据提供变革性工具。最终，这将提供流变学、地质年代学和地球化学的限制，这些限制来自与俯冲有关的岩石，这些岩石可以与远程观测相结合（例如，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。