Graduate Thesis Or Dissertation
 

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/70795b09m

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  • The North Muddy Mountains are located in southern Nevada, about 65 km northeast of Las Vegas and near the eastern boundary of the Basin and Range province. The north-south-trending range block is bounded on the east and west, respectively, by east- and west-dipping, high-angle normal faults. Sevier age contractional and Cenozoic age extensional structures are present in the range. The Summit thrust and Willow Tank thrust crop out, respectively, on the southwest and northeast sides of the North Muddy Mountains. A newly mapped thrust segment connects the Summit and Willow Tank thrusts. It juxtaposed Jurassic on Cretaceous age rocks. The most recent displacement on the thrust is bracketed between 95.8 +/- 3.5 Ma (age of youngest deformed rocks) and 93.1 +/- 3.4 Ma (age of oldest overlying undeformed beds). These numbers indicate an Albian to Turonian(?) age range for the thrust. The Summit-Willow Tank thrust sheet was later folded by a northwest-southeast-trending, southwest inclined fold train by displacement on the Arrowhead fault, a Miocene and possibly younger(?) extensional structure. The oldest (Albian) synorogenic deposits in the area contain exotic clasts of formations that were not involved in local thrusting; the debris was transported eastward from older thrust sheets. Younger (Cenomanian) synorogenic beds are composed of Mesozoic age clasts at the base of the section, grading to early paleozoic age clasts near the top (reverse clast stratigraphy). This succession represents progressively deeper erosion of thrust sheets during thrusting. The younger synorogenic beds do not contain exotic clasts from older, more westerly, thrust sheets. This observation suggests that local thrust sheets formed highlands that shut off the westerly source provenance. Rotation of horst and graben blocks on Cenozoic normal and oblique-slip faults caused dismembering of older Sevierage fold-thrust structures, and in some cases refolded them into new orientations. Seismic reflection sections show wedge-shaped sedimentary beds, indicating that range-bounding normal faults formed half-grabens. The normal faults appear to be listric impling that the net slip on these faults is a measure of the regional horizontal extension.
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