Collaborative Research: RUI: Reconstructing the Plastic-to-Brittle Exhumation History of the Taiwan Metamorphic Core

台湾代表了地球上最活跃的构造环境之一。该岛标志着吕宋火山弧和亚洲被动边缘之间的碰撞，几十年来，碰撞推动了地球动力学模型来解释世界各地许多山带的演变。这种碰撞驱动了台湾山带的变形和活动隆升。由于非常迅速的隆升和高侵蚀速率，台湾的变质核暴露在台湾中部山脉的核心及其东部边缘。在这里，一个由美国和台湾科学家和学生组成的联合小组正在探索这样一种观点，即变质岩的挖掘是通过延伸而不是通常被调用的碰撞驱动的缩短模型来促进的。研究人员将检查变质岩的几何形状和活动断层的运动模式，以确定岩石被挖掘的机制。除了提供关于造山过程的新见解外，该项目还通过妇女和代表性不足的少数民族参与STEM来推进预期的社会成果；(b)通过本科生和研究生培训以及为台湾本科生举办的研讨会，发展一支多元化的、具有全球竞争力的STEM劳动力队伍；(c)通过国际合作加强伙伴关系。更具体地说，本计画的目的是记录台湾变质岩心从塑到脆的挖掘历史。中部山脉东部的变质岩心（田南奥片岩）具有难以在稳态双辐合造山带背景下解释的特征；当前流行的模式。在山带大部分地区，变质片理陡倾，形成西东东、东西倾的区域解理扇。靠近碰撞缝合线（纵向谷），这种简单的模式被打破，最年轻的变质叶理通常是平缓倾斜的。此外，该地区迄今观测到的中尺度断层大多为正位移，并与地壳地震记录的北东-西向伸展方向一致。研究人员的目的是验证台湾东部正位移断层和剪切带可容纳变质岩心同步碰撞发掘的假设。这将需要系统地记录田南奥片岩中最年轻的变质构造和复印脆性结构的几何和运动学，并在地震构造和地震层析成像的约束下建立塑性-脆性变形模式和持续变形之间的关系。由美国和台湾科学家以及研究生和本科生组成的研究小组将收集变质岩结构数据和定向岩石样本，用于岩石学和XCT分析。还将收集韧性剪切带和叠印脆性结构（如断层和节理）的运动学数据。现有震源机制目录将以台湾中央气象局资料所产生的新震源机制加以补充。结果将与地震层析成像和地震构造对活动变形的限制相结合，以更好地了解台湾出土背后的机制。S变质岩心；

Taiwan represents one of the most active tectonic environments on Earth. The island marks the collision between the Luzon volcanic arc and the passive margin of Asia and for decades the collision has motivated geodynamic models to explain the evolution of many mountain belts around the world. This collision drives deformation and active uplift of the Taiwan mountain belt. Because of the very rapid uplift and high erosion rates the metamorphic core of Taiwan is exposed in the core of Taiwan's Central Range and its eastern margin. Here, a joint team of U.S. and Taiwanese scientists and students is exploring the idea that exhumation of the metamorphic rocks is facilitated by extension rather than the collision-driven shortening model that is usually invoked. The researchers will examine the geometry of the metamorphic rocks and the movement patterns of active faults to determine the mechanisms by which the rocks are exhumed. In addition to providing new insights into mountain building processes, the project advances desired societal outcomes through participation of women and underrepresented minorities in STEM; (b) development of a diverse, globally competitive STEM workforce through undergraduate and graduate student training plus a workshop for Taiwan undergraduate students; and (c) increased partnerships through international collaboration.More specifically, the objective of this project is to document the plastic-to-brittle exhumation history of the metamorphic core of Taiwan. The metamorphic core (the Tananao schist) in the eastern Central Range is marked by characteristics that are difficult to explain in the context of a steady-state, doubly-vergent orogenic wedge; the current prevailing model. In most parts of the mountain belt, metamorphic foliations are steeply dipping, forming a regional cleavage fan that is east dipping in the west and west dipping in the east. Close to the collisional suture (Longitudinal Valley) this simple pattern breaks down and the youngest metamorphic foliation is commonly gently dipping. Moreover, most mesoscale faults observed to date in this area record normal displacement and accommodate NE-SW extension, the same extension direction as recorded in crustal earthquakes. The researchers aim to test the hypothesis that normal displacement faults and shear zones accommodate syn-collision exhumation of the metamorphic core in eastern Taiwan. This will entail systematically documenting the geometry and kinematics of the youngest metamorphic fabrics and overprinting brittle structures in the Tananao Schist, and establishing the relation between the plastic-to-brittle deformation patterns and ongoing deformation as constrained by seismotectonics and seismic tomography. The research team composed U.S. and Taiwanese scientists and graduate and undergraduate students will collect metamorphic fabric data, and oriented rock samples for petrographic and XCT analyses. Kinematic data for ductile shear zones and overprinting brittle structures, e.g., faults and joints, will also be collected. The existing catalog of earthquake focal mechanisms will be supplemented with new mechanisms generated from Taiwan Central Weather Bureau data. The results will be integrated with seismic tomography and seismotectonic constraints on active deformation to better understand the mechanisms behind exhumation of Taiwan?s metamorphic core.