Collaborative Research: Thermochronology of Dominant Thrust Sheets in the Sevier Fold Thrust Belt, Utah and Nevada: Determining Fault Timing and Slip Rates

确定褶皱-冲断带内断层滑动的时间和速率，确定变质腹地前陆逆冲作用与地壳增厚的关系，确定冲断作用与前陆盆地沉降的关系，对于理解沿会聚板块边界的山系演化具有重要意义。本研究将结合详细的热年代学研究和相关盆地中逆冲板和沉积岩的结构分析，以确定Sevier褶皱-逆冲带中两个“主导”逆冲板的起始时间和断裂持续时间、断层滑动率和侵蚀历史，这两个逆冲板分别是犹他州北部的Willard逆冲板和内华达州南部及邻近加利福尼亚州的Wheeler Pass逆冲板。这些逆冲层为量化断层滑动和热历史提供了绝佳的机会，因为它们暴露得很好，位移大（20-50公里），构造起伏大（5公里），并且包含适合应用热年代学方法的岩石。将使用三种采样策略来阐明热、侵蚀和断层滑动历史：多种测温仪（白云母和钾长石40Ar/39Ar，锆石和磷灰石裂变轨迹，以及锆石U-Th/He，覆盖400°至100°C的封闭温度范围）将结合起来确定冲断片中各个位置的温度-时间路径；将完成沿推力片垂直断面冷却年龄的变化，以限制挖掘率；断层滑动方向沿水平样带的年龄变化将用于估计断层滑动速率。热年代学数据将与一系列断层几何形状的热模型进行比较，这些断层几何形状受构造分析、边界条件和侵蚀历史的限制，这些模型受冲断片沉积和相关前陆盆地沉积的沉积物分析的限制。研究结果将有助于进一步了解塞维尔带逆冲作用的起始时间、褶皱冲断带缩短与变质腹地复杂构造史之间的时间相关性，以及作为塞维尔带发育关键机械组成部分的主导逆冲片的侵位沿走向变化。采用详细采样方案的多个温度计的应用将作为一个案例研究，用于如何可靠地估计推力系统的热历史，这对于了解油气成熟度和寻找潜在的油气聚集至关重要。该项目是内华达大学拉斯维加斯分校和韦伯州立大学研究人员的合作成果。作为该项目的一部分，两校的研究生和本科生将进行合作研究，并通过科学会议和出版物交流成果，提供重要的科学培训。这些工作也有助于认识和勘探大盆地的油气和矿产资源。

Determining the timing and rates of fault slip within fold-thrust belts, relations between foreland thrusting and crustal thickening in metamorphic hinterlands, and relations between thrust loading and foreland basin subsidence are critical for understanding evolution of mountain systems along convergent plate boundaries. This study will combine detailed thermochronology studies and structural analysis of thrust sheets and sedimentary rocks in associated basins to determine timing of initiation and duration of faulting, fault slip rates, and erosion histories of two "dominant" thrust sheets in the Sevier fold-thrust belt, the Willard thrust sheet in northern Utah and the Wheeler Pass thrust sheet in southern Nevada and adjacent California. These thrust sheets provide an exceptional opportunity to quantify fault slip and thermal histories as they are well exposed, have large displacements (20-50 km), exhibit significant (5 km) structural relief, and contain rocks suitable for application of thermochronology methods. Three sampling strategies will be used to elucidate thermal, erosion, and fault slip histories: multiple thermochronometers (muscovite and K-feldspar 40Ar/39Ar, zircon and apatite fission track, and zircon U-Th/He that cover a range of closure temperatures from 400° to 100°C) will be combined to determine temperature-time paths for individual locations in thrust sheets; variations in cooling ages along vertical transects through thrust sheets will be completed to constrain exhumation rates; and variations in ages along horizontal transects in the fault slip direction across thrust sheets will be used to estimate fault slip rates. Thermochronologic data will be compared with thermal models for a range of fault geometries constrained by structural analysis, boundary conditions, and erosion histories constrained by analysis of sediments shed from thrust sheets and deposited in associated foreland basins. Results will improve understanding of the poorly defined timing of initiation of thrusting in the Sevier belt, temporal correlations between shortening in the fold-thrust belt and the complex tectonic history of the metamorphic hinterland, and along strike variations in emplacement of the dominant thrust sheets that were key mechanical components in development of the Sevier belt. The application of multiple thermochronometers using detailed sampling schemes will serve as a case study for on how to robustly estimate thermal histories in thrust systems, which is critical for understanding hydrocarbon maturation and targeting potential hydrocarbon accumulations. The project is a collaborative effort between researchers at the University of Nevada-Las Vegas and Weber State University. As part of the project, graduate students and undergraduate students from both universities will conduct collaborative research and communicate results through scientific meetings and publications, providing significant scientific training. The work may also contribute to understanding/exploration for hydrocarbon and mineral resources in the Great Basin.