Collaborative Research: Testing Theories of Synconvergent Extension in the Hinterland of the Sevier Orogen

人们越来越认识到，高海拔山脉和大陆高原，由于其高海拔的地壳缩短，通常在板块会聚期间经历伸展。 尽管这一过程得到了广泛的认识，但同会聚伸展的原因目前还不完全清楚，仍然是大陆构造学中的一个突出问题。 本研究评估的过程，导致同会聚延伸在美国西部的白垩纪塞维尔造山带，与其他山区带的应用。 对三种常被引用的同会聚伸展机制进行了评价：（1）构造增厚地壳的热松弛，导致部分熔融和壳幔分离;（2）双重断裂导致超临界造山锥的局部地壳增厚;（3）岩石圈地幔的拆沉。 这些过程中的每一个都有可预测的影响，这些影响正在通过对塞维尔造山带腹地的两个地方的研究进行测试：犹他州西北部和爱达荷州南部的筏河-阿尔比恩-松鸡溪山脉，以及加州东南部的葬礼山脉。 这些都是理想的领域，以评估过程相关的同收敛扩展。 如先前的研究表明，中生代造山作用的长期变质和变形记录保存完好，这是因为在定义明确的新生代伸展剪切带和拆离断层之间和之下的中生代组构的保留很少或不存在热叠印。 作为该研究项目的一部分，我们正在进行详细的现场测绘，结构和运动学分析，定量变质热压法和PT路径测定石榴石，原位离子微探针钍-铀-铅测年的独居石，Luticium-Haftenium和钐-Neoconium石榴石地质年代学，和氩-氩热年代学。 这种综合的方法是必要的：（1）确定压力-温度-时间路径，（2）评估早期逆冲埋藏和随后的同会聚伸展的运动学，（3）通过比较压力-温度-时间路径与数值模拟预测的那些来检验同会聚伸展的假设，以及（4）关联腹地和前陆演化。 本研究中采用的多种地质年代学方法为改进Luticium-Haftenium和Samarium-Neodenium定年石榴石方法的温度依赖性校准提供了基础。 这项综合研究代表了三所大学和主要大学在构造地质学、变质岩石学、数值热模拟、同位素地球化学和地质年代学方面的研究成果。 拟议的工作是在各级充分协作和一体化的。 在这项研究中开发的信息和技术正在传播到构造，岩石学和地球化学社区。 该项目为四名研究生和四名本科生提供研究培训，其中包括代表不足的团体成员。 学生参与者作为研究生和本科生论文进行本研究的重要组成部分，并获得实地观察，数据采集和数据分析的经验。 他们通过在大学研究博览会和地质会议上的演讲，为传播这项研究的结果做出了贡献，并在经评审的期刊上发表了科学论文。 学生通过接触本研究的调查方法，以及理解和整合合作者的数据和分析的需要，从项目的协作性质中受益。 这项研究补充了内华达大学拉斯维加斯分校在松鸡溪和阿尔比恩山脉的大理石峰和米尔克里克地区的两个地质学夏令营，并为葬礼山所在的死亡谷国家公园的科学知识库做出了贡献。

It is increasingly well recognized that high altitude mountains and continental plateaus, which owe their high elevations to crustal shortening, commonly undergo extension during plate convergence. Despite widespread recognition of this process, the causes of synconvergent extension are currently incompletely understood and remain an outstanding problem in continental tectonics. This study evaluates the processes that led to synconvergent extension in the Cretaceous Sevier orogen in the western United States, with application to other mountain belts. Three frequently cited mechanisms for synconvergent extension are being evaluated: (1) thermal relaxation of tectonically thickened crust, leading to partial melting and decoupling of crust from mantle; (2) localized crustal thickening resulting from duplex faulting leading to supercritical orogenic taper, and (3) the delamination of lithospheric mantle. Each of these processes has predictable effects that are being tested through studies of two localities within the hinterland of the Sevier orogen: the Raft River-Albion-Grouse Creek ranges in northwestern Utah and southern Idaho and the Funeral Mountains in southeastern California. These are ideal areas to evaluate processes related to synconvergent extension. As prior studies indicate, protracted metamorphic and deformational records of Mesozoic orogenesis are well preserved due to minimal or absent thermal overprints and preservation of Mesozoic fabrics between and beneath well-defined Cenozoic extensional shear zones and detachment faults. As part of this research project we are conducting detailed field mapping, structural and kinematic analysis, quantitative metamorphic thermobarometry and PT path determination on garnet, in situ ion microprobe Thorium-Uranium-Lead dating of monazite, Luticium-Hafnium and Samarium-Neodymium garnet geochronology, and Argon-Argon thermochronology. This integrated approach is necessary to (1) determine pressure-temperature-time paths, (2) evaluate the kinematics of early thrust burial and subsequent synconvergent extension, (3) test hypotheses for synconvergent extension by comparing the pressure-tempearture-time paths to those predicted by numerical simulations, and (4) correlate hinterland and foreland evolutions. The multiple geochronologic methods employed in this study provide a basis for refining the calibrations of temperature dependence of the Luticium-Hafnium and Samarium-Neodymium methods of dating garnet. This integrated study represents a research effort between three universities and principal investigors with expertise in structural geology, metamorphic petrology, numerical thermal modeling, isotope geochemistry and geochronology. The proposed work is fully collaborative and integrated at all levels. Information and techniques developed in this research is being disseminated to tectonic, petrologic, and geochemical communities. This project provides research training for four graduate students and four undergraduates, including members of underrepsented groups. The student participants conduct important components of this research as graduate and undergraduate theses, and gain experience in making field observations, data acquisition, and data analysis. They contribute to the dissemination of the findings of this study through presentations at university research expositions and geologic conferences, and contribute to scientific papers in refereed journals. Students benefit from the collaborative nature of the project through exposure to the investigative methods of this study, and the need to understand and integrate data and analysis from collaborators. The research complements two University of Nevada-Las Vegas geology summer field camps in the Marble Peak and Mill Creek areas of the Grouse Creek and Albion Mountains, and contributes to the scientific knowledge base for Death Valley National Park, where the Funeral Mountains are located.