Collaborative Research: Evaluating the role of terrane accretion on the evolution of indenter corner fault systems, an example from the eastern Himalaya

大陆构造板块的碰撞产生了地球上一些最高的地形，最深的沉积盆地和最可能发生大地震的地区。为了解释这些独特的板块边界是如何演变的，地质学家通常会模拟一个刚性构造板块与一个较弱的构造板块碰撞并压痕的碰撞。最近对喜马拉雅东部和阿拉斯加的观测表明，自然界中的凹痕板块并非完全是刚性的，特别是当它们包含了地质历史上先前碰撞产生的地壳块块时。这意味着活动断层系统也可能在凹陷板块和凹陷板块内变形（并产生地震），从而改变了地球科学家理解大陆碰撞带内板块边界断层的方式。该项目将研究喜马拉雅东部复杂的构造环境，这是一个天然实验室，用于验证先前的增生地体从根本上改变碰撞带边缘的活动断层系统的假设。这项研究将解决2018年美国国家科学基金会社区构造学研究愿景文件中概述的三大挑战，并将加强美国科学家与印度多所大学和研究中心的研究人员以及促进公众科学素养的当地非政府组织之间的国际联系。该项目将通过对分析方法进行正式的实验室间比较，为美国和印度本科生共同组织两次研讨会，以及开展K-12教育推广活动，进一步促进美国和国际合作伙伴之间的知识转移。该项目还将支持两名早期职业教师，并促进两名研究生和两名本科生的充分参与，这些学生将通过旨在扩大传统上代表性不足的群体在地球科学领域的参与的项目招募。造山带是高地壳应变的区域，在凹进板块碰撞的边缘适应从收敛到走滑运动的转变。几十年来，构造学的研究主要集中在碰撞带缩进板块内的应变分配，而忽视了缩进板块内应变分配的重要影响，特别是银质地块的吸积对缩进角断交演化的作用。来自东喜马拉雅和阿拉斯加造山带的观测表明，沿碰撞带两侧的转换断层的银块地的增生可能导致“双重碰撞”，在这种碰撞中，曾经稳定的断层交叉点变成了不稳定的三重交叉点，改变了压痕角断层系统的运动学和上板变形的模式。为了评估地表增生对碰撞造山作用的广泛影响，这个为期3年的项目将重建喜马拉雅东部压头角的一个三结的运动历史。该项目重点研究了诺亚丁丁断层的运动学历史。诺亚丁丁断层是喜马拉雅东部压痕角中心的一个关键构造，位于印度-欧亚碰撞带、印度和缅甸地体之间的俯冲带以及缅甸-欧亚转换带之间。本项目将通过野外填图、锆石U-Pb年代学、断层运动学分析、诺阿顶顶断裂上盘磷灰石裂变径迹、锆石裂变径迹和40Ar/40Ar热年代学的热运动学模拟相结合，对诺阿顶顶断裂晚新生代运动史进行约束。验证这一假设，即在大陆压痕角内的银块集中应变，将有助于解释相同构造环境下压痕角之间的结构风格差异（例如，喜马拉雅东部和西部压痕角之间的曲率差异），也有助于解释不同构造环境下压痕角之间的相似性（例如，阿拉斯加南部和喜马拉雅东部）。这是一种思考压痕构造的新方法，可以提供一个互补的视角，进一步帮助将阿拉斯加和喜马拉雅造山带的研究联系起来。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The collision of continental tectonic plates produces some of the highest topography, deepest sedimentary basins, and highest potential for large earthquakes on Earth. To explain how these unique plate boundaries evolve, geologists commonly simulate a collision between a rigid tectonic plate that collides with and indents a weaker tectonic plate. Recent observations from the eastern Himalaya and Alaska instead suggest that indenting plates in nature are not entirely rigid, particularly when they contain pieces of crustal blocks accreted from prior collisions in the geologic past. This implies that active fault systems may also deform (and generate earthquakes) within the indenting plate as well as the indented plate, changing the way geoscientists understand plate boundary faults within continental collision zones. This project will study the complex tectonic setting of the eastern Himalaya, a natural laboratory for testing the hypothesis that prior accreted terranes fundamentally change the active fault systems at the margins of a collision zone. This research will address three Grand Challenges outlined in a 2018 NSF Community Vision Document for Tectonics research and will strengthen international ties between US scientists and researchers at multiple Indian universities and research centers, as well as a local non-governmental organization promoting public scientific literacy. This project will further facilitate knowledge transfer between US and international partners by conducting a formal interlaboratory comparison of analytical methods, co-organizing two workshops for US and Indian undergraduate students, and developing K-12 educational outreach. This project will also support two early career faculty and promote the full participation of two graduate and two undergraduate students who will be recruited through programs designed to broaden participation of traditionally underrepresented groups in the geosciences.Orogenic syntaxes are regions of high crustal strain that accommodate the transition from convergence to strike-slip motion at the margins of an indenting plate collision. For several decades, Tectonics research has focused on strain partitioning within the indented plate of a collision zone, this focus has neglected the important influence of strain partitioning within the indenting plate, and in particular, the role of sliver terrane accretion on the evolution of indenter corner fault intersections. Observations from both the eastern Himalayan and Alaskan orogens suggest that the accretion of sliver terranes along transform faults flanking collision zones can lead to a ‘double collision’ where a once-stable fault intersection changes into an unstable triple junction, altering the kinematics of indenter corner fault systems and the pattern of upper plate deformation. To evaluate the broader influence of terrane accretion on collisional orogenesis, this 3-year project will reconstruct the kinematic history of a triple junction in the eastern Himalayan indenter corner. This project focuses on the kinematic history of the Noa Dihing Fault, a key structure at the center of the eastern Himalaya indenter corner that juxtaposes the Indian-Eurasian collision zone with the subduction zone between Indian and the Burma Terrane, as well as the Burma-Eurasia transform zone. This project will constrain the late Cenozoic kinematic history of the Noa Dihing Fault through a combination of field mapping, zircon U-Pb geochronology, fault kinematic analysis, and thermo-kinematic modeling of apatite fission-track, zircon fission track and 40Ar/40Ar thermochronology in the Noa Dihing Fault hanging wall. Testing this hypothesis that sliver terranes concentrate strain within continental indenter corners will help to explain differences in structural style between indenter corners in the same tectonic setting (e.g. differences in the curvature between the eastern and western Himalayan indenter corners) and also relate similarities between indenter corners in different tectonic settings (e.g. southern Alaska and the eastern Himalaya). This is a new way of thinking about indenter tectonics and could provide a complementary perspective that builds further helps to link research in Alaskan and Himalayan orogens.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.