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、变质腹地前陆逆冲与地壳增厚的关系、逆冲载荷与前陆盆地沉降的关系，对于了解会聚板块边界的山系演化是至关重要的。这项研究将结合详细的热年代学研究和对相关盆地中的逆冲片和沉积岩的结构分析，来确定Sevier褶皱冲断带中两个主要的冲断片，即犹他州北部的Willard冲断片和内华达州南部和邻近的加利福尼亚州的Wheeler Pass冲断片的起始时间和持续时间、断层滑动速率和侵蚀历史。这些逆冲断块提供了一个绝佳的机会来量化断层滑动和热历史，因为它们暴露得很好，具有大的位移(20-50公里)，显示出显著的(5公里)构造起伏，并含有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：将结合多种热计时仪(白云母和钾长石40Ar/39Ar，锆石和磷灰石裂变径迹，以及涵盖400°到100°C范围内的锆石U-Th/He)来确定逆冲片中各个位置的温度-时间路径；将完成沿逆冲片垂直断面的冷却年龄变化，以限制折返速率；以及将利用沿逆冲片断层滑动方向水平断面的年龄变化来估计断层滑动速率。热年代学数据将与一系列断层几何的热模型进行比较，这些断层几何受构造分析、边界条件和侵蚀历史的约束，受逆冲断块沉积并沉积在相关前陆盆地中的沉积物分析所约束。这些结果将有助于人们更好地理解塞维尔带内推覆构造的启动时间，褶皱冲断带的缩短与变质腹地复杂的构造历史之间的时间相关性，以及作为塞维尔带发展中的关键机械组件的主要逆冲断块沿走向的侵位变化。使用详细采样方案的多个温度计时器的应用将作为如何可靠地估计逆冲系统中的热历史的案例研究，这对于理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的研究人员共同努力的成果。作为该项目的一部分，两所大学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。这项工作还可能有助于了解/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.