3-D MODELLING OF THRUST FAULTING AND FOLDING IN THE EAST RANGE, SONOMA RANGE, AND GOLCONDA SUMMIT, NORTH-CENTRAL NEVADA: INSIGHTS INTO THE GEOMETRY, TIMING, AND SIGNIFICANCE OF THE GOLCONDA THRUST

Computer-aided three-dimensional modelling of the structural architecture in an area centred on the Sonoma Range of northern Nevada provides insights into the Paleozoic and Mesozoic thrust faulting, folding, and cross-cutting relationships in the region. To construct the model, a series of fifteen cross sections oriented approximately WNW\ESE (perpendicular to major structural trends) across the study volume were created. The sections were digitized and incorporated into a GIS, and correlative faults in the sections were linked with 3-D surfaces to project structures throughout the volume.

Six distinct thrust faults are present in the study volume, produced by the Antler Orogeny, Sonoma Orogeny, and/or progressive Mesozoic contraction. All thrust faults have been affected by regional scale SSW-plunging folds. The axial trace of a first-order synform extends across Golconda Summit (Golconda Synform), and the adjacent antiform traces across the northern Sonoma Range (Sonoma Antiform). The Clear Creek Thrust System (CCTS) exposed in the Sonoma and East ranges includes a series of W-vergent thrusts that imbricate rocks as young as late Triassic in age. The CCTS is truncated to the south by the Golconda Thrust, which either post-dated the CCTS or served as the roof thrust of a duplex involving the CCTS. Our analysis indicates: (1) significant post-Late Triassic shortening occurred in the region, probably in Early to Middle Jurassic time, suggesting that the Mesozoic contractional front propagated across north-central Nevada in a relatively continuous manner, rather than jumping across this region; and (2) the Golconda Thrust in it’s type locality is post-Late Triassic in age, and may have been kinematically linked to the Luning-Fencemaker system and other Early to Middle Jurassic contractional structures.