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，这种碰撞激发了地球动力学模型来解释世界各地许多山脉带的演变。这种碰撞驱动了台湾山带的变形和主动隆升。台湾变质核由于快速的隆升和高侵蚀率，暴露在台湾中央山脉的核心和东部边缘。在这里，一个由美国和台湾科学家和学生组成的联合团队正在探索这样一种想法，即变质岩的折返是由延伸而不是通常引用的碰撞驱动的缩短模型促进的。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，以确定岩石被挖出的机制。除了提供对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群体参与STEM，推动取得预期的社会成果;（B）通过本科生和研究生培训以及为台湾本科生举办的讲习班，培养一支多样化、具有全球竞争力的STEM劳动力队伍;及（c）透过国际合作，增加伙伴关系。更具体地说，本计画的目标是记录台湾变质核的塑性-脆性折返历史。变质核（Tananao片岩）在中央山脉东部的特点是难以解释的背景下，稳定状态，双收敛造山楔，目前流行的模式。在山带的大部分地区，变质面理都是陡倾的，形成了一个西向东倾、东向西倾的区域劈理扇。靠近碰撞缝合线（纵谷），这种简单的模式被打破，最年轻的变质叶理通常是轻轻倾斜。此外，迄今为止在该地区观测到的大多数中尺度断裂记录了正常位移，并容纳NE-SW延伸，与地壳地震记录的延伸方向相同。研究人员的目的是测试假设，正常位移断层和剪切带容纳同碰撞折返的变质核在台湾东部。这将需要系统地记录最年轻的变质组构的几何形状和运动学，并在Tananao片岩中叠加脆性结构，并建立塑性-脆性变形模式与受地震构造和地震层析成像约束的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组构数据，并对岩石样品进行岩相学和XCT分析。韧性剪切带和叠加脆性构造的运动学数据，例如，断层和节理，也将被收集。现有的地震震源机制目录将补充台湾中央气象局数据产生的新机制。研究结果将结合地震层析成像和地震构造对活动变形的限制，以更好地了解台湾折返的机制。的变质核。

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.