Collaborative Research: Roles of lithology and water on deep continental crustal rheology from a natural setting and laboratory experiments

合作研究：自然环境和实验室实验中岩性和水对深部大陆地壳流变学的作用

• 批准号: 2234125
• 负责人: Kevin Mahan
• 金额: $ 46.45万
• 依托单位: University of Colorado at Boulder
• 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=2234125&HistoricalAwards=false
• 关键词: Collaborative; Research; Roles; lithology; water

Earthquakes are generally observed at shallow depths (15 km) in Earth’s upper continental crust or at greater depths (50-660 km) in subducting oceanic plates. Recent discoveries of rocks that are only formed by melting on fault surfaces during seismic slip events in the deep (20-50 km) continental crust indicate that earthquakes can occur in zones previously thought to be aseismic. The mechanisms that can cause earthquakes to occur in aseismic shear zones are not understood. However, recent observations indicate that the strength of many minerals in these rocks is sensitive to the amount of water entrained inside the mineral grains and that water loss may strengthen them. Researchers from the University of Colorado Boulder and the University of Akron will perform an integrated series of modeling, field, and laboratory-based investigations to quantify how water loss affects the strength of a deep crustal fault zone. They will perform field-based investigations of the processes operating in the Cora Lake Fault Zone, Saskatchewan, Canada, measure water contents in all of the rocks in the fault zone, and perform experiments to characterize the effect of water content on the strength of quartz, one of the dominant phases in the fault zone. The results of these studies will be used to create a predictive model of the processes that caused the deep crustal earthquakes. Desired societal outcomes will include advancement of our understanding of the processes that cause earthquakes, as well as the support of an early-career post-doctoral researcher, graduate students, and undergraduate students.This project will advance our understanding of the rheology of “dry” deep continental crust using three complementary approaches. First, the researchers will conduct field-based and microstructural characterization of a kilometer-scale shear zone exhumed from 35–25 km paleodepths in the Canadian shield. The structure hosts synkinematic pseudotachylyte that developed under nominally anhydrous granulite- to upper amphibolite-facies conditions. The work will include water content measurements on nominally anhydrous minerals, particularly quartz and feldspar, to correlate their rheology to dry, damp, or wet deformation experiments and rheologic modeling. Second, pressure-stepping deformation experiments will determine the effects of water content and fugacity on quartz creep strength. Shear experiments on low water content quartzites will also be conducted to compare microstructure and deformation/recovery mechanisms with observations from the shear zone. Third, viscoelastic numerical modeling using dry and wet mineral flow laws, with refined parameters from the above experiments, will test the hypothesis that stress enhancement due to lithologic and water content variations led to episodic brittle failure and pseudotachylyte generation in the shear zone. The models will also guide field work by highlighting areas in the shear zone where more accurate characterization of field relationships is needed.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.

通常在地球上部连续地壳的浅深度（15 km）处观察到地震，或者在俯冲的海洋板上更大的深度（50-660 km）。最新发现的岩石仅在深（20-50 km）大陆地壳中的地震滑动事件中融化而形成的岩石发现，这表明在以前被认为是无向震动的区域中发生地震。不了解可能导致地震发生的机制。但是，最近的观察结果表明，这些岩石中许多矿物质的强度对矿物晶粒内部的水量敏感，并且水分流失可能会增强它们。科罗拉多大学博尔德大学和阿克伦大学的研究人员将进行一系列集成的建模，现场和基于实验室的研究，以量化水流失如何影响深层地壳断层区的强度。他们将对加拿大萨斯喀彻温省Cora湖断层区域中运行的过程进行基于现场的研究，测量断层区所有岩石中的水含量，并进行实验以表征水含量对石英强度的影响，石英的强度，石英的强度，这是断层区域中的主要阶段之一。这些研究的结果将用于创建导致深层地震的过程的预测模型。期望的社会成果将包括我们对引起地震过程的理解以及对早期职业后博士后研究人员，研究生和本科生的支持。该项目将通过三种完整的方法来提高我们对“干燥”深层甲壳的理解。首先，研究人员将对加拿大盾牌中从35–25 km古兴趣的挖掘的公里尺度剪切带进行基于现场的和微观结构表征。该结构的合成假鸟酯具有名义上无水颗粒至上闪石面的条件。这项工作将包括关于名义上无水矿物（尤其是无水矿物）的水含量测量，以将其流变学与干燥，潮湿或湿变形实验和流变学建模相关联。其次，压力变形实验将确定水含量和逸度对石英蠕变强度的影响。还将进行低水含量石英的剪切实验，以将微结构和变形/恢复机制与剪切区的观测值进行比较。第三，使用干燥和湿的矿物流量定律进行粘弹性数值建模，并具有上述实验的精制参数，将检验以下假设：由于岩性和水分含量变化引起的应力增强导致了剪切区中的脆性脆性衰竭，并导致了剪切区中的假望台。模型还将通过突出剪切区域中需要更准确地表征现场关系的区域来指导现场工作。该奖项反映了NSF的法定任务，并通过使用基金会的知识分子优点和更广泛的影响评估标准来评估，被认为是珍贵的支持。