Collaborative Research: Unraveling Protracted Tectonic Reactivation in Cordilleran Metamorphic Core Complexes: Funeral Mountains, California

断裂带成为可在地质历史中重新激活的长期软弱带的倾向，对地球-S地壳中流体的运移和油气的形成、经济矿产和地下水资源、地震灾害和山带的演化起着重要作用。从1.6亿到5000万年前，美国西部在构造上与今天的南美洲西部相似，后者的特点是高海拔山脉(安第斯山脉)形成于活跃俯冲的大洋板块上方的大陆地壳中。当北美西部的俯冲停止时，开始了一个新的广泛地壳伸展的制度，导致古代山脉带深层表面的局部暴露。这个项目将考察死亡谷国家公园的殡仪山，主要调查人员假设那里记录了建山和扩建的周期。特别是，他们假设，最初负责大量埋藏和增厚地壳的同一断层(逆冲断层)在岩石挖掘到地表期间被重新激活了两次。他们进一步认为，逆冲断层的重新激活可能是美国西部的一个常见现象，这解释了其他山脉中许多类似的情况。殡葬山脉的岩石是检验这一假说的理想之选，因为它们暴露在极好的环境中，而且有丰富的岩石可供研究。该项目将实现NSF确定的许多社会利益：(1)帮助美国保持在全球科学、技术、工程和数学(STEM)劳动力队伍中的竞争力和领导地位；参与该项目的学生(3名研究生和5名本科生)将在STEM学科中发展高水平的专业知识和团队合作经验；(2)通过在专业会议和出版物上发表演讲，向学术界传播研究成果，并通过在死亡谷自然历史协会、拉斯维加斯自然历史博物馆和内华达州地质学会的会议上发言，提高公众的科学素养；(3)作为合作研究工作的一部分，在两所大学之间发展研究伙伴关系，并在每个机构发展研究基础设施；(4)研究人员通过有针对性的招聘努力，寻求让妇女和代表性不足的学生充分参与STEM教育。这一建议的论点是，美国西部的许多第三纪拆离断层和剪切带重新激活了早期变形的断层或亚平面地带。死亡谷地区的殡葬山脉变质核杂岩是塞维尔-拉拉米德腹地的理想地点，用来评估构造再激活在变质核杂岩发展中的作用，以及解决有关第三纪伸展之前的构造史的重要细节。我们推测，边界峡谷拆离断层在中新世经历了40多公里的顶部-西北滑动，是侏罗纪主要的反向滑动逆冲推覆的最后一次重新激活，导致了下盘的深埋和区域变质作用。我们提出了一种多方面的方法，通过沿变质和应变梯度的详细研究来评估长期构造重新激活的假说，其中包括：(1)野外填图和结构分析，(2)富含石英岩石的岩相学、显微结构和运动学分析，(3)应用岩石年代学(激光烧蚀分裂流电感耦合等离子体质谱)来确定副矿物(变质钛铁矿、独居石、辉石和锆石过度生长)和石榴石角闪岩中石榴石的Lu-Hafn定年，以及(4)确定变质条件和延长的压力-温度路径来评价晚期埋藏史。主要剪切带之间可能存在的坡度不一致，以及区域逆冲引起的古倾角。对构造再活动的认识对于了解Sevier-Larama造山带的早侏罗世和白垩纪历史、造山过程中收缩和伸展的规模和分布以及造山后伸展的幕式性质具有重要意义。

The propensity for fault zones to become long-lived zones of weakness that can be reactivated during geologic history plays a significant role in the migration of fluids in Earth?s crust and formation of hydrocarbon, economic mineral and ground water resources, seismic hazards, and the evolution of mountain belts. From 160 to 50 million years ago, the western U.S. was tectonically similar to modern day western South America, which is characterized by high elevation mountains (the Andes) that formed in the continental crust above an actively subducting oceanic plate. When subduction ceased along western North America, a new regime of widespread crustal extension began, resulting in localized exposures at the surface of deep levels of the ancient mountain belt. This project will examine the Funeral Mountains in Death Valley National Park, which the principal investigators hypothesize records the cycle of mountain building followed by extension. In particular, they hypothesize that the same fault (a thrust fault) initially responsible for substantial burial and thickening of the crust was reactivated twice during the exhumation of the rocks to the surface. They further argue that the reactivation of thrust faults may be a common phenomenon in the western U.S., explaining many similar occurrences in other mountain ranges. Rocks in the Funeral Mountains are ideal for testing this hypothesis due to excellent exposures and abundant rocks suitable for study. This project will accomplish many benefits to society as identified by NSF: (1) helping the U.S. maintain competitiveness and leadership in the global Science Technology Engineering and Mathematics (STEM) workforce; students who participate in the project (three graduate students and five undergraduates) will develop high-level expertise and teamwork experience in a STEM discipline; (2) increased public scientific literacy by dissemination of findings to the academic community through presentations at professional conferences and publications, and to the general public and Death Valley enthusiasts by presenting at meetings of the Death Valley Natural History Association, the Las Vegas Natural History Museum, and the Nevada Geological Society; (3) development of research partnerships between two universities as part of collaborative research efforts, and the development of research infrastructure at each institution; and; (4) the investigators seek to engage the full participation of women and underrepresented students in STEM education through targeted recruiting efforts.Reactivation and tectonic inheritance are long-recognized phenomena, important to our understanding of how the continental lithosphere deforms. The thesis of this proposal is that many Tertiary detachment faults and shear zones in the western US reactivate faults or sub-planar zones of earlier deformation. The Funeral Mountains metamorphic core complex of the Death Valley region represents an ideal locality in the Sevier-Laramide hinterland to evaluate the role of tectonic reactivation in the development of metamorphic core complexes, as well as to resolve important details regarding the tectonic history that predates Tertiary extension. We hypothesize that the Boundary Canyon detachment fault, which underwent greater than 40 kilometers of top-the northwest slip in the Miocene, formed as the last reactivation of a major Jurassic thrust of opposite slip that was responsible for deep burial and regional metamorphism of the footwall. We propose a multi-faceted approach to evaluate the hypothesis of protracted tectonic reactivation through detailed studies along the metamorphic and strain gradient that includes: (1) field mapping and structural analysis, (2) petrographic, microstructural, and kinematic analyses aided by Electron Backscatter Diffraction analysis of quartz-rich rocks, (3) applying petrochronology (Laser Ablation Split Stream Inductively Coupled Plasma Mass Spectrometry) to date accessory minerals (metamorphic titanite, monazite, xenotime, and zircon overgrowths) and Lutetium-Hafnium dating of garnet in garnet amphibolites, and (4) determining the metamorphic conditions and prograde pressure-temperature paths to evaluate the prograde burial history, possible grade discordances across major shear zones, and the regional thrust-induced paleodip. Recognition of tectonic reactivation has important implications for understanding the older Jurassic and Cretaceous history of the Sevier-Laramide orogen, the magnitude and distribution of contraction and extension that occurred during orogenesis, and the episodic nature of post-orogenic extension.