CAREER: Understanding Major Intracontinental Strike-slip Faults from the Lower Crust's Perspective: Tibetan Insights from the Canadian Shield

大陆碰撞和沿岩石圈规模(数百公里长)的陆内走滑断层的变形之间的关系仍然存在激烈的争论。争论仍在继续，因为尽管我们知道地表这类重要的断层，但我们对这些构造在下地壳中是如何工作的知之甚少。在这个项目中，关于应变局部化程度、流变非均质性的横向程度以及深部主要陆内断裂的物理性质的问题，将通过研究暴露良好的地壳深剪切带及其围岩，即加拿大地盾西部400公里长的陆内润滑河剪切带(出土于约30至40公里的古深度)来“就地”回答。初步资料支持这样的假设，即在约1.92~1.90Ga的时间里，油脂河剪切带的下地壳NW向熔融减弱，同时，油脂河剪切带的下地壳东南方向脱水而强烈。这个？流变学的二分法？可能类似于青藏高原边缘陡峭的地形梯度和主要陆内断裂系统下的下地壳，例如阿尔金山和龙门山山脉。该项目将从下地壳的角度提供基于现场的约束，限制流变非均质性在促进跨主要陆内走滑断裂的应变局部化方面的作用。预期的成果包括：(1)解决了格里斯河剪切带及其围岩中变质构造岩的压力-温度条件和路径；(2)利用独居石的电子探针原位Th-U-全铅测年，验证了变形、剪切和部分熔融的同时性；该项目的广泛影响包括：(1)实施6-8年级教师培训和强化计划；(2)通过课堂访问和小组讨论向公众宣传陆内系统中的断层和地震。这些努力将直接影响居住在新马德里地震带未暴露的陆内断层附近的教师和学生？落基山脉以东地震最活跃的地区。将向教师提供两个专业发展暑期学院(讲习班+实地考察)，利用由国际学校开发的以探究为基础的模块。这些单元的实施和评估将影响阿肯色州的中学地球科学框架(并通过在线传播单元在全国范围内)。这些努力将与阿肯色大学的数学和科学教育中心合作。培训和教育将提供给至少一名博士生、一名硕士研究生和几名本科生，他们将全面参与研究和推广工作。该项目直接影响到阿肯色大学新的地球科学博士项目。EarthScope社区也有望受益，因为该项目使用了加拿大地盾中暴露的地壳深剪切带，以帮助我们了解陆内走滑断层的结构、流变性和时间，因为它可能存在于莫霍面附近的下地壳中。

The relationship between continental collision and deformation along lithosphere-scale (hundreds of km-long) intracontinental strike-slip faults remains intensely debated. Debate persists because despite what we know about this important class of faults at the surface, we know comparatively little about how these structures work in the lower crust. Questions regarding the degree of strain localization, the lateral extent of rheological heterogeneities, and the physical nature of major intracontinental faults at depth will be answered "in situ" in this project by studying a well-exposed deep crustal shear zone and its wall rocks, i.e., the 400 km-long intracontinental Grease River shear zone in the western Canadian Shield (exhumed from ~30 to 40 km-paleodepths). Preliminary data support the hypothesis that at ca. 1.92-1.90 Ga, lower crust NW of the Grease River shear zone was melt-weakened at the same time that lower crust SE of the Grease River shear zone was dehydrated and strong. This ?rheological dichotomy? may be analogous to lower crust beneath the steep topographic gradients and major intracontinental fault systems that mark the margins of the Tibetan Plateau, e.g., the Altyn Tagh and Longmen Shan ranges.This project will provide field-based constraints on the role of rheological heterogeneity in facilitating strain localization across a major intracontinental strike-slip fault from the lower crust's perspective. Anticipated results include: (1) resolving the Pressure-Temperature conditions and paths for metamorphic tectonites in the Grease River shear zone and its wall rocks, (2) testing the contemporaneity of deformation, shearing, and partial melting using in situ Th-U-total Pb dates on monazite via EPMA, and (3) constraining a 500 m.y. history of shear zone reactivation via high-precision ID-TIMS U-Pb dates on zircon from a suite of cross-cutting and variably-deformed dikes.Broader impacts of this project include: (1) implementing a program of 6th-8th grade teacher preparation and enhancement, and (2) public outreach via classroom visits and panel discussions that are all focused on faulting and earthquakes in intracontinental systems. These efforts will directly impact teachers and students who live in the immediate vicinity of unexposed intracontinental faults of the New Madrid seismic zone ? the most seismically active region east of the Rocky Mountains. Two professional development summer institutes (workshops + field trips) will be provided to teachers utilizing inquiry-based modules to be developed by the PI. Implementation and assessment of these modules will impact middle school Earth Science frameworks in Arkansas (and nationally via on-line dissemination of the modules). These efforts will be in collaboration with the University of Arkansas' Center for Math and Science Education. Training and education will be provided to at least one Ph.D. student, one M.S. student, and several undergraduate students who will be integrally involved in the research and outreach efforts. This project directly impacts the new geoscience Ph.D. program at the University of Arkansas. Benefits to the EarthScope community are also anticipated, as this project uses an exposed deep crustal shear zone in the Canadian Shield to inform our understanding of the structure, rheology, and timing of a major intracontinental strike-slip fault as it may have existed in the lower crust near the Moho.