Williams, Stewart Alexander, authorSingleton, John, advisorRidley, John, committee memberLaituri, Melinda, committee member2020-01-132020-01-132019https://hdl.handle.net/10217/199744Zip file contains Plate 1 - map.The Jurassic Minas Viejas Formation is host to a Late Cretaceous to early Paleogene-aged décollement in the Sierra Madre Oriental, Mexico. The Minas Viejas Formation is dominated by rheologically-weak evaporite that accommodated thin-skinned deformation, forming the Sierra Madre Oriental fold-thrust belt with minimal deformation to the underlying Triassic-Jurassic red beds. Thin-skinned shortening above the décollement temporally transitioned to thick-skinned shortening, resulting in exhumation of the décollement and development of the Potosí uplift, one of the largest and well exposed thick-skinned uplifts in the orogen. Detailed geologic mapping and structural analysis provide insight into the geometry and kinematics of the Potosí uplift, and (U-Th)/He thermochronometry and vitrinite reflectance record the burial history and timing of exhumation associated with the uplift. Thick-skinned deformation involved folding of sub-décollement strata into a NNW-SSE-striking anticlinorium, development of cleavage, ENE-WSW directed thrust faulting, conjugate strike-slip faulting, and formation of ENE-WSW-striking extension fractures associated with barite mineralization. These structures consistently record ENE-directed subhorizontal shortening. Shortening is directed ~062° in the southern part of the uplift and ~077° in the northern part of the uplift. Thick-skinned deformation modified pre-existing geometries of thin-skinned folds involving Cretaceous overburden strata above the Jurassic evaporite décollement. Zircon (U-Th)/He cooling dates (ZHe) and vitrinite reflectance data indicate that the entire evaporite décollement was buried to ≥185°C, consistent with development of phyllitic fabrics in the basal part of the Minas Viejas Formation. Paleocene to mid-Eocene zircon (U-Th)/He cooling dates in the Triassic-Jurassic red beds below the evaporite décollement directly record the timing of exhumation associated with thick-skinned deformation, and suggest that the thick-skinned uplift was a continuation of earlier thin-skinned shortening as opposed to a distinct tectonic event. A zircon (U-Th)/He date from the southern Potosí uplift is ~66 Ma, whereas ZHe dates in the northern part of the uplift range from ~49–43 Ma. Two samples from the nearby Aramberri uplift to the south of the Potosí uplift have mean ZHe dates of ~63–54 Ma. The transition from thin- to thick-skinned shortening may be attributed to the evolution of mechanical stratigraphy in the décollement. Thin-skinned detachment folding resulted in significant migration of evaporite away from synclinal keels, effectively eliminating a planar weak zone at the base of the décollement and creating salt welds between carbonates or shales within the décollement with underlying red beds. The along-strike differences in timing of thick-skinned exhumation and the shortening directions may also be attributed to differences in mechanical stratigraphy. Thicker intervals of evaporite in the northern part of the uplift allowed thin-skinned shortening to continue while the southern part of the uplift transitioned to thick-skinned shortening as the weak evaporite décollement was exhausted. As a result, stress-strain trajectories in the northern part of the uplift refracted clockwise towards the area with more propagation of deformation. Our findings provide a new insight into the geometry, kinematics, and timing of deformation associated with the Potosí uplift, and may provide a framework for studying other thick-skinned uplifts in the Sierra Madre Oriental, and more generally orogenic belts that record a transition in deformation styles.born digitalmasters thesesZIPPDFengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.Text