Author(s): Carson Jocelyn
Mentor(s): Alex Tye
Institution UTech
The structure of the Beaver Dam Mountains, in Southern Utah, is a classic locality for understanding the tectonics of low-angle normal fault systems and how they relate to extension in the Basin and Range province of the western US. The structure of the Beaver Dam Mountains is dominated by an east-dipping, homoclinal package of basement and Phanerozoic sedimentary rocks, interpreted to have been uplifted by isostatic rebound of a low-angle normal footwall (called the rolling hinge model). The goal of this project is to collect new data and re-examine the evidence to determine the tectonic history of the Beaver Dam Mountains. Data collection was focused on the Castle Cliff Detachment System and its hanging wall and footwall, which were examined via an extensive geologic mapping campaign to confirm the lithology and structure, specifically looking for evidence of pre-Neogene deformation. Samples were also collected for apatite and zircon thermochronometric dating and analysis. Collected data were plotted for visualization and analysis in a geographic information system (GIS). The results of the mapping were several areas that showed evidence of thrusting and some overturned folds. From what has been observed in the field there is evidence suggesting that there was shortening occurring before the extension began. Reconstructed cross-sections will help to determine the most likely structural model for the area. The area is interesting due to the nonconformity between Precambrian metamorphic basement on the west side of the range and Phanerozoic sedimentary rocks stratigraphically above, similar to the layers seen at the bottom of the Grand Canyon. The areas of interest all have detachment faults that are indicators of the extension that has occurred since the time that the Basin and Range province rifting began. While the detachments prove that sub horizontal faulting has taken place, some locations seemed to have been folded during or after extension. The preliminary conclusion is that the area very well could have undergone shortening during the Sevier orogeny, of which this locale would have been on the far eastern edge. Moving onward with this project the answer will start to become apparent with the production of cross-sections and the results of the test samples. This project is important because it will help us to understand the complicated history and structure of the area more which will help mitigate seismic hazards and may lead to the discovery of mineral resources in the future.