Chapter 9: Tertiary normal faults superimposed on Mesozoic thrusts, Quinn Canyon and Grant Ranges, Nye County, Nevada
John M. Bartley, Gayle Gleason, 1990. "Chapter 9: Tertiary normal faults superimposed on Mesozoic thrusts, Quinn Canyon and Grant Ranges, Nye County, Nevada", Basin and Range Extensional Tectonics Near the Latitude of Las Vegas, Nevada, Brian P. Wernicke
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The Grant and Quinn Canyon ranges lie in a part of the eastern Great Basin commonly designated as the hinterland of the Mesozoic Sevier thrust belt. Published mapping of the northern and central Grant Range indicates that virtually all of the low-angle faults in that area are Cenozoic normal faults. However, our recent mapping in the southern Grant and northern Quinn Canyon ranges confirms the presence of Mesozoic thrust faults that have been overprinted by normal faulting.
Four major north-striking faults are exposed in an east-west transect across the study area. Two faults are east-vergent thrusts of probable Cretaceous age. We name the structurally higher thrust the Sawmill thrust and the lower the Rimrock thrust. Each thrust emplaced unmetamorphosed to very weakly metamorphosed Upper Cambrian to Lower Ordovician miogeoclinal strata upon Devonian rocks. The thrusts have the ramp-flat geometries and internally shortened hanging walls typical of foreland thrust belts. Together the thrusts accommodated at least 10 km of horizontal shortening. The age of thrusting is not yet constrained precisely but is most likely Cretaceous.
The actual thrust contacts are preserved only locally because two major west-dipping Cenozoic normal fault systems, the Oligocene Wadsworth Ranch fault system and the Miocene Little Meadow fault system, commonly excise the thrusts. A consequence of thrust excision is that local older-on-younger relations occur across the normal faults. Both of the normal fault systems are complex networks of intersecting planar segments. Geometric relations of the Wadsworth Ranch fault system indicate hanging-wall transport toward the southwest. By contrast, slip along the Little Meadow fault system appears to have been directed mainly west to west-northwest. This suggests a clockwise rotation of the extension direction from one phase to the next.
The thrusts in the Grant and Quinn Canyon ranges probably correlate along strike northward with the Mesozoic Eureka belt of folds and thrusts, which lies to the west of the Sevier hinterland. This belt of thrusts is probably similar in age to the frontal Sevier belt and, when effects of Tertiary extension are restored, is located less than 200 km west of the Sevier thrust front. Based on these relations and the fact that Cordilleran-type foreland thrust belts in Canada and the Andes are both about 200 km wide, we suggest that much of the Sevier “hinterland” is actually a part of the Sevier foreland thrust belt that has been intensely extended in Cenozoic time. The intense Cenozoic extensional overprint that obscures the thrust-belt structures is responsible for most of the distinctive features of the Sevier hinterland. Therefore, to refer to this region as the “Sevier hinterland” is inaccurate and misleading, and we favor abandonment of the term.