MESOZOIC SYN-METAMORPHIC STRUCTURE OF THE PANAMINT MOUNTAINS WITH IMPLICATIONS FOR RECONSTRUCTION OF NEOGENE EXTENSION

The Mesozoic structure of the Panamint Mountains has been used repeatedly as a template for reconstructing Neogene extension in Death Valley, yet most of the range has been mapped at 1:62,500 or smaller allowing divergent models of the extensional history. Here we report on results of high-resolution 3D mapping of the western Panamint metamorphic complex that resolves structural geometries to meter and decimeter level over the bulk of the metamorphic core. High resolution mapping was made possible by mapping onto point clouds generated using Structure-from-Motion/Multiview Stereo (SM) photogrammetry developed during experiments comparing ground-based, drone-based, and chartered aircraft-based imaging, aided by an existing terrestrial LiDAR survey in parts of the range. Zircon U-Pb geochronology provides important age constraints on the deformation, although more geochronology is needed. The metamorphic assemblage is complexly deformed with ubiquitous large finite strains. The main ductile deformation produced a prominent continuous cleavage and lineation that track finite strain, it is demonstrably pre-Laramide (~80Ma) based on cross-cutting two mica granitoids, and it is associated with two generations of isoclinal folds that form type 2 and type 3 interference patterns at outcrop and map scale. The kinematics of these structures is obscure because of overprinting, but the prominent NS stretching lineation is margin parallel suggesting possible strike-slip. The main fabric was refolded during the Laramide to form a train of NS trending, open to tight, upright to steeply inclined folds with an associated crenulation cleavage and are equivalent to the folds shown on old published maps; they have nothing to do with extension as has been postulated by some studies. Collectively our observations suggest that the entire central Panamint range was subjected to deformational sequence analogous to supracrustal overprints described by Pavlis et al. (2014, Geosphere) east of Death Valley indicating any restoration of Neogene extension would require restoring the central Panamints south of the deformation front of the younger thrusting; yet the kinematics of the deformation (NS stretching) raises further questions on the tectonics of the pre-Laramide deformation.