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: 1550154
• 负责人: Thomas Hoisch
• 金额: $ 24.96万
• 依托单位: Northern Arizona University
• 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 2021-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1550154&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.

断裂带倾向于成为长期存在的软弱带，可以在地质历史中重新激活，这在地球流体的迁移中起着重要作用。地壳与油气形成、经济矿产与地下水资源、地震灾害、山带演化等。从1亿6千万年前到5千万年前，美国西部的构造与现在的南美洲西部相似，其特点是高海拔山脉（安第斯山脉）形成于大陆地壳之上，是一个积极俯冲的海洋板块。当北美西部的俯冲作用停止时，一种新的广泛的地壳伸展开始了，导致古山带深层表面的局部暴露。该项目将考察死亡谷国家公园的葬礼山，主要研究人员假设记录了山的建造和扩展的循环。特别是，他们假设同一条断层（逆冲断层）最初对地壳的大量埋藏和增厚负有责任，在将岩石挖掘到地表的过程中，这条断层被重新激活了两次。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种普遍现象，这可以解释其他山脉中许多类似的现象。丧葬山的岩石是检验这一假设的理想场所，因为那里有很好的暴露条件和丰富的适合研究的岩石。该项目将实现美国国家科学基金会确定的许多社会效益：(1)帮助美国保持在全球科学技术工程和数学（STEM）劳动力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）将培养STEM学科的高水平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研究成果向学术界传播，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表研究成果向公众和死亡谷爱好者传播，从而提高公众的科学素养；(3)发展两所大学之间的研究伙伴关系，作为合作研究的一部分，并在每所大学发展研究基础设施；和;(4)调查人员寻求通过有针对性的招聘工作，让女性和代表性不足的学生充分参与STEM教育。活化和构造继承是长期以来公认的现象，对我们理解大陆岩石圈如何变形很重要。本文的论点是美国西部许多第三纪拆离断裂和剪切带重新激活了早期变形的断裂或次平面带。死亡谷地区的丧葬山变质核杂岩是Sevier-Laramide腹地评价构造活化在变质核杂岩发育中的作用以及解决第三纪伸展前构造历史的重要细节的理想地点。我们推测，边界峡谷滑脱断层在中新世经历了超过40公里的顶部西北滑动，是侏罗纪逆滑逆冲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，通过沿着变质和应变梯度的详细研究来评估长期构造再激活假说，包括：(1)野外制图和构造分析；(2)利用电子背散射衍射分析对富石英岩石进行岩相学、微观结构和运动学分析；(3)应用岩石年代学（激光烧蚀裂流电感耦合等离子体质谱法）对副矿物（变质钛矿、独一石、xenotime和锆石）进行年代测定；(4)确定变质条件和前向压力-温度路径，以评价前向埋藏史、主要剪切带之间可能的等级不一致以及区域逆冲古倾角。认识构造再活动对认识西维尔—拉拉amide造山带早侏罗世和白垩纪历史、造山过程中收缩和伸展的大小和分布以及造山后伸展的幕式性质具有重要意义。