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

确定褶皱逆冲带内断层滑动的时间和速率、前陆逆冲与变质腹地地壳增厚之间的关系以及逆冲载荷与前陆盆地沉降之间的关系对于理解沿着会聚板块边界的山地系统的演化至关重要。 这项研究将结合详细的热年代学研究和相关盆地中的逆冲片和沉积岩的结构分析，以确定塞维尔褶皱逆冲带中两个“主要”逆冲片、犹他州北部的威拉德逆冲片和内华达州南部和邻近加利福尼亚州的惠勒山口逆冲片的起始时间和持续时间、断层滑移速率和侵蚀历史。这些逆冲片为量化断层滑移和热历史提供了绝佳的机会，因为它们暴露良好，具有较大的位移（20-50公里），表现出显着的（5公里）结构起伏，并且包含适合热年代学方法应用的岩石。将使用三种采样策略来阐明热、侵蚀和断层滑移历史：将组合多个测温计（白云母和钾长石 40Ar/39Ar、锆石和磷灰石裂变径迹以及涵盖 400° 至 100°C 闭合温度范围的锆石 U-Th/He），以确定逆冲片中各个位置的温度-时间路径；将完成沿着冲断层的垂直横断面的冷却年龄的变化，以限制折返率；沿逆冲片断层滑动方向的水平横断面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结构分析、边界条件和侵蚀历史的限制，而侵蚀历史则受冲断片脱落并沉积在相关前陆盆地的沉积物分析的限制。结果将提高对塞维尔带逆冲起始时间的不明确、褶皱逆冲带缩短与变质腹地复杂构造历史之间的时间相关性，以及作为塞维尔带发育的关键力学组成部分的主要逆冲片沿走向变化的理解。使用详细采样方案的多个测温计的应用将作为如何稳健地估计推力系统中的热历史的案例研究，这对于了解碳氢化合物的成熟度和瞄准潜在的碳氢化合物聚集至关重要。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结果，提供重要的科学培训。这项工作还可能有助于了解/勘探大盆地的碳氢化合物和矿产资源。

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.