Joint 118th Annual Cordilleran/72nd Annual Rocky Mountain Section Meeting - 2022

Paper No. 16-8
Presentation Time: 10:45 AM


POLCINO, Christina1, HOUCHIN, Shane2, SINHA, Simmi3, JORY, Billyjack4 and WERNICKE, B.P.2, (1)Pasadena City College, 1570 E Colorado Blvd, Pasadena, CA 91106, (2)Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, (3)University of Colorado, Boulder, Boulder, CO 80309, (4)University of California, Santa Barbara, Santa Barbara, CA 93106

The Mormon Mountains region in southern Nevada has been mapped extensively, uncloaking a complex geologic history that records the overprint of the Cretaceous thrust fault system along the Sevier front by Miocene extensional detachments. Two previously mapped detachment faults, the Mormon Peak and Petroglyph detachments, are the result of considerable extension throughout the region. Although their origin has been debated, they are generally regarded as middle Miocene low-angle normal faults. The relationship between the Mormon Peak and petroglyph detachments is exposed in a previously unmapped area in the southwestern part of the range a few kilometers northwest of Moapa Peak. We conducted five days of map traverses of a ca. 10 km^2 area of highly complex structure and stratigraphy. The mapping revealed a major area of exposure of the Mormon Peak allochthon and underlying Mormon Peak detachment that is contiguous with exposures to the north. The allochthon includes a thrust duplex developed within generally northwest-tilted Cambrian Nopah Formation at its structural base, overlain by more coherent Ordovician, Devonian, and Mississippian strata, cut by numerous normal faults that do not penetrate the smoothly contourable detachment. Our preliminary mapping results and structural analysis indicate that this segment of the Mormon Peak detachment is coplanar and therefore correlative with the Petroglyph detachment, which collectively juxtapose the regionally developed Mormon thrust duplex (in Cambrian strata) with either the sub-duplex Mormon thrust plate or the Sevier authochthon. The new mapping therefore expands the mapped areal extent of the Mormon Peak allochthon from the western Tule Springs Hills to the Moapa Peak area, and provides further evidence to support the origin and evolution of the Mormon Peak detachment as a major Miocene extensional fault along the Sevier front in southern Nevada.