STRUCTURAL DETAILS OF THE CHICAGO PASS-SHAW THRUST SYSTEM IN THE NOPAH-RESTING SPRING RANGE: A KEY FOR RESOLVING EXTENSIONAL MODELS IN THE DEATH VALLEY REGION

Pavlis et al. (2014) presented evidence that kinematically distinct fold-thrust systems are present in the Nopah-Resting Spring region in eastern Death Valley and that intersection lines between these systems were key to reconstructing the system. This study builds on that hypothesis with a detailed analysis of the Shaw thrust-Chicago Pass thrust system in the northern Nopah Range, a critical marker within the system. This study focused on the Shaw thrust which is difficult to correlate to the east across Pahrump Valley or to the west across Chicago Valley. We mapped the area initially using high resolution orthophotos draped on a digital elevation model using QGIS and ArcGIS, and then field checked the site in critical problem areas. Because the Shaw thrust places dolomite on limestone, we also used remote sensing techniques to distinguish these rocks using multispectral ASTER data. Work in progress will evaluate these remote sensing interpretations as well as experiment using a gigapan camera together with Structure from Motion photogrammetry to build a 3D terrain model for further interpretation. Preliminary results suggest that units previously mapped as coherent lithologic units are instead landslide deposits that obscure much of the trace of the Shaw Thrust. Also, the Shaw thrust sheet is ~13 meters thick at the location of Shaw Mine as it converges with the Chicago Pass thrust to the west and much of its original thickness has been removed due to erosion. Consequently, it does not run along the length of the Chicago Pass as has been previously interpreted and only crops out to the very north and the southwest. Our working hypothesis is that much of what is mapped as the Shaw thrust is either a series of landslide deposits or has been eroded away, and the Shaw thrust ends at a branch line against the Chicago Pass thrust in the northern Nopah range. This implies that the Shaw thrust does not correlate to the Resting thrust to the west, suggesting the Resting thrust is truncated by the younger Nopah Peak/Gerstley thrust system. Additionally, the Shaw thrust does not terminate into the Chicago Pass thrust under Pahrump Valley. Instead it is the equivalent of the Lee Canyon thrust in the Spring Mountains.