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

合作研究：解开科迪勒拉变质核复合体中长期的构造重新激活：加利福尼亚州葬礼山

• 批准号: 1550158
• 负责人: Michael Wells
• 金额: $ 29.57万
• 依托单位: University of Nevada Las Vegas
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1550158&HistoricalAwards=false
• 关键词: Collaborative; Research; Unraveling; Protracted; Tectonic

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.

断层带倾向于成为长期存在的薄弱地带，可以在地质历史期间重新激活，在地球流体的迁移中起着重要的作用？地壳与油气的形成、经济矿产和地下水资源、地震灾害和山地带的演化。从1.6亿到5000万年前，美国西部在构造上与现代南美洲西部相似，其特征是高海拔山脉（安第斯山脉）形成于活跃俯冲的海洋板块之上的大陆地壳中。 当沿北美西部沿着的俯冲作用停止时，一个新的广泛地壳伸展状态开始了，导致了古老山脉带深层表面的局部暴露。这个项目将研究死亡谷国家公园的葬礼山，主要研究人员假设记录了山脉建造和扩展的周期。 特别是，他们假设，最初造成大量埋藏和地壳增厚的同一断层（逆冲断层）在岩石向地表折返的过程中被重新激活了两次。他们进一步认为，逆冲断层的复活可能是美国西部的一种常见现象，解释了其他山脉中许多类似的现象。葬礼山脉的岩石是测试这一假设的理想选择，因为它们具有良好的暴露性和丰富的岩石适合研究。 该项目将实现NSF确定的许多社会效益：（1）帮助美国保持全球科学技术工程和数学（STEM）劳动力的竞争力和领导地位;参与该项目的学生（三名研究生和五名本科生）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的演讲向学术界传播研究结果，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;（3）发展两所大学之间的研究伙伴关系，作为合作研究工作的一部分，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，寻求让女性和代表性不足的学生充分参与STEM教育。重新激活和构造继承是长期公认的现象，对我们理解大陆岩石圈如何变形很重要。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带。死亡谷地区的葬礼山变质核杂岩代表了塞维尔-拉腊米腹地的一个理想地点，以评估变质核杂岩发展中构造活化的作用，以及解决有关第三纪伸展之前的构造历史的重要细节。我们假设，边界峡谷拆离断层，经历了超过40公里的顶部-西北滑在中新世，形成作为最后一次复活的主要侏罗纪逆冲断层的相反滑，负责深埋和区域变质的下盘。我们提出了一种多方面的方法，通过沿着变质和应变梯度的详细研究来评估长期构造复活的假设，其中包括：（1）野外测绘和结构分析，（2）岩相学、显微结构和运动学分析，并借助富石英岩石的电子背散射衍射分析，（3）应用岩石年代学（激光烧蚀分流电感耦合等离子体质谱法）测定辅助矿物（变质钛铁矿、独居石、磷钇矿和锆石过生）和石榴石斜长岩中石榴石的镥-铪定年，（4）确定变质条件和逆冲推覆压力-温度路径，以评价逆冲推覆埋藏史、主要剪切带之间可能存在的品位不一致和区域逆冲推覆古倾角。认识到构造活化具有重要意义，了解老侏罗纪和白垩纪的历史Sevier-Laramide造山带，规模和分布的收缩和伸展发生在造山作用，以及造山后的阶段性伸展。