PRELIMINARY NEOTECTONICS ANALYSIS, SOUTHERN RED ROCK FAULT, TENDOY RANGE, CHUTE CANYON, SW MONTANA

At Chute Canyon in SW Montana, we began a detailed neotectonics study of the Quaternary fault slip history of the ~9 km-long trace of the southern Red Rock fault which bounds the eastern flank of the Tendoy Range. This NW-SE-trending range and its east-bounding normal fault may represent the modern expression of Basin and Range-style extension that sits in the northern arm of the Yellowstone parabola in the wake of the migrating Yellowstone “hot spot” swell. Our one-week-long project was part of the 2022 summer field geology course at the University of Houston. Our study was done in cooperation with UNAVCO, providing UAV and dGPS support, and MBMG, providing OSL and TCN sample support. We used the following methods: 1) A literature review was conducted to understand context, basic geology, fault physics, and paleoseismology. 2) UAV imagery, plus field mapping, focused on mapping bedrock, active fault scarps, triangular facets, colluvial wedges, steep- and gentle-gradient alluvial fans, and stream terraces. A preliminary pre-, post-, and syn-rupture chronology was reconstructed. 3) Two OSL, one TCN depth profile and ten TCN boulders samples were collected from the T1 terrace cut by the fault and the Chute Creek Canyon fan that post-dates it. 4) dGPS fault scarp profiling and diffusion analysis was done. We obtained preliminary rupture ages that range from 3-15 ka by using fault scarp diffusion modeling. 5) cGPS velocities from 6 sites that span this fault segment processed by the University of Nevada-Reno Geodesy Lab were used to assess fault-normal velocity gradients and elastic strains. Both V_up and V_fault-normal show the expected patterns of strain accumulation across an elastically locked normal fault. 6) Finally, preliminary earthquake hazard and risk assessments were conducted by examining the history of earthquakes, slip rate estimates, published recurrences, and using our cGPS geodesy constraints. This study provided hands-on instruction, and the initial data and results in what will hopefully be a longer-term, more comprehensive study of this and other active faults in the region.