Collaborative Research: Fluid infiltration of the continental crust during Laramide flat-slab subduction: a unique tectonic setting

合作研究：拉拉米德平板俯冲期间大陆地壳的流体渗透：独特的构造环境

• 批准号: 2318411
• 负责人: Thomas Hoisch
• 金额: $ 34.79万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2026-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2318411&HistoricalAwards=false
• 关键词: Collaborative; Research; Fluid; infiltration; continental

This study investigates an ancient example of a continental margin setting that involves shallow-angle or flat-slab subduction, that is, where an oceanic plate dives beneath a continental margin at a shallow angle. Rocks from an ancient example, which was active 80 to 40 million years ago, are preserved in southern California and Arizona. Comparison of the ancient example with mathematical simulations of this setting shows that they do not accurately simulate important aspects. For example, studies have shown that rocks at the top of the oceanic plate got much hotter than predicted by the simulations, and that above the oceanic plate, where cooling is predicted, some rocks melted. The investigators will collect data from rocks in the ancient setting that were once located just above the descending oceanic plate. This will lead to improved simulations and a better understanding of similar modern tectonic settings, many of which pose significant seismic risk to human populations. The project supports the participation of undergraduates in the research at Northern Arizona University and the University of Wisconsin at Madison. In addition, the project supports four early career PhDs, three of whom are members of an underrepresented group. This project will investigate the conditions, timing, and fluid sources of deep-crustal fluid infiltration during Laramide flat-slab subduction in southeastern California (Big Maria Mountains) and western Arizona (Cemetery Ridge). Cemetery Ridge exposes metamorphosed oceanic sediments (Orocopia Schist) containing blocks of mantle peridotite transported ~300 km inland by Laramide low-angle subduction. The Big Maria Mountains exposes suprasubduction crustal rocks, also inferred to have been located ~300 km inboard of the paleotrench. Both areas display strong evidence for Laramide fluid-driven metamorphism and metasomatism. Chemical changes associated with metasomatism will be evaluated by comparing the bulk-rock chemistry of metasomatised rocks to unmetamorphosed protoliths. The pressure-temperature conditions of metasomatism will be investigated using Raman spectroscopy of carbonaceous material thermometry and quartz in garnet elastic barometry and thermodynamic modeling. The timing of fluid infiltration will be determined by laser ablation split stream mass spectrometry of titanite, monazite, and zircon. The source of fluids will be evaluated using stable isotopes of oxygen and boron. The new data will provide a basis for constraining model parameters needed for mathematical simulation of the system for which independent estimates are unavailable (frictional coefficient, subduction angle, suprasubduction viscous heating, and critical temperature for thermal weakening within the subduction channel). The project will achieve broader impacts through efforts that target the development of a diverse workforce in the geosciences and increasing public scientific literacy. Presentations of the research to the public will be made by undergraduate participants at research symposia hosted at both participating institutions. In addition, the project supports career advancement for four early career PhDs, three of whom are members of an underrepresented group.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.

这项研究调查了一个涉及浅角度或平板俯冲的大陆边缘环境的古老例子，即海洋板块以浅角度俯冲到大陆边缘下方。南加州和亚利桑那州保存有 80 至 4000 万年前活跃的古代岩石。将古代示例与此设置的数学模拟进行比较表明，它们没有准确地模拟重要方面。例如，研究表明，海洋板块顶部的岩石比模拟预测的要热得多，而在预测冷却的海洋板块上方，一些岩石融化了。研究人员将从古代环境中的岩石中收集数据，这些岩石曾经位于下降的海洋板块上方。这将改进模拟并更好地理解类似的现代构造环境，其中许多对人类构成重大的地震风险。该项目支持北亚利桑那大学和威斯康星大学麦迪逊分校的本科生参与研究。 此外，该项目还支持四名早期职业博士，其中三名是代表性不足群体的成员。 该项目将调查加利福尼亚州东南部（大玛丽亚山脉）和亚利桑那州西部（公墓岭）拉拉米德平板俯冲期间深部地壳流体渗透的条件、时间和流体来源。墓地山脊暴露出变质海洋沉积物（Orocopia 片岩），其中含有通过拉拉米德低角度俯冲作用向内陆输送约 300 公里的地幔橄榄岩块。大玛丽亚山脉暴露了超俯冲地壳岩石，也推断其位于古海沟内侧约 300 公里处。这两个地区都显示出拉拉酰胺流体驱动的变质作用和交代作用的有力证据。将通过比较交代岩石与未变质原岩的块体岩石化学来评估与交代作用相关的化学变化。将利用碳质材料测温的拉曼光谱和石榴石弹性气压测定中的石英以及热力学模型来研究交代作用的压力-温度条件。流体渗透的时间将通过钛矿、独居石和锆石的激光烧蚀分流质谱测定来确定。将使用氧和硼的稳定同位素来评估流体来源。新数据将为无法获得独立估计的系统数学模拟所需的模型参数（摩擦系数、俯冲角、超俯冲粘性加热和俯冲通道内热弱化的临界温度）提供基础。该项目将通过致力于发展地球科学领域的多元化劳动力和提高公众科学素养来实现更广泛的影响。本科生参与者将在两个参与机构举办的研究研讨会上向公众介绍该研究成果。此外，该项目还支持四名早期职业博士的职业发展，其中三名是代表性不足群体的成员。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。