Northwesterly displacement of the Sierra Nevada with respect to the Great Basin in the western US Cordillera has been ongoing for the last 12 to 15 Ma. This motion is accommodated by a complicated and incompletely understood belt of deformation along the western margin of the Great Basin that links major, misaligned strike-slip faults in eastern California and western Nevada. Based on previous research and our preliminary work, we have identified that the deformed belt underlies a region of nearly 15,000 km2 and contains large tectonic blocks that both translate toward the northwest as the crust is pulled apart and also undergo vertical-axis rotations of 20° to 90°. In this project, we will provide a better understanding of the dimensions of the tectonic blocks, how far they have moved laterally, to what degree they experienced vertical-axis rotation, and the spatial-temporal pattern of deformation. Much of the western borderland of North America and many parts of other continents around the world reside in similar tectonic settings and record comparable histories of deformation. This study will provide the opportunity to better understand how and to what degree the translation and rotation of large crustal blocks is accommodated as the continental crust is fragmented in response to the relative movement of lithospheric plates.
Crustal response to displacement transfer in structural stepovers linking misaligned segments of large-magnitude transcurrent faults is accommodated by components of translational and rotational displacement and strain and results in complex three-dimensional arrays of structures. The mechanisms by which rotational and translational strain are accommodated either by rigid-blocks and/or by distributed strain and to what degree the translational and rotational processes are coupled in space-time are poorly understood. In this study, we integrate detailed and regional geologic mapping with thermochronologic, structural, and paleomagnetic analysis to unravel the history of transcurrent structures separating the Sierra Nevada and central Great Basin. The objective of the work is to characterize transcurrent and high-angle normal fault displacement, estimate slip on low-angle detachment faults, and assess the relation between translational deformation and differential rotation. Our research results will provide the needed detailed understanding of the spatial and temporal pattern of deformation and supply the constraints to differentiate between coeval and serial translational and rotational deformation histories within the stepover system and provide the means to assess whether or to what degree rotation is accommodated by rigid-body motion or distributed strain processes.
