MESOZOIC DUCTILE DEFORMATION IN THE PANAMINT MOUNTAINS: SEVIER CONTRACTION OVERPRINTED BY LARAMIDE AGE HINTERLAND-VERGENT FOLDING

New 3D mapping and geochronology in the central Panamint Mountains provide new constraints on the regional Mesozoic contractional history. Neogene extension exposed a partial crustal section of a Mesozoic low-P/T metamorphic assemblage ranging from an upper amphibolites facies on the west to subgreenschist facies east of the range crest. New field techniques using 3D mapping on a terrain model derived from TLS and SfM photogrammetry allow 3D geometric resolutions of a few cm in our structural observations. Our analyses indicate two prominent ductile deformational events and a domainal third event. The earliest deformation (D₁) produced a prominent continuous cleavage (S₁) with an associated NNW trending stretching lineation. This LS fabric varies from a low-strain phyllitic cleavage oblique to bedding near the range crest to a high-strain LS crystallographic and shape fabric with object ellipticities in excess of 50 at the deepest structural levels. S₁ is axial planar to prominent outcrop and larger scale folds (F₁) that range from tight to close folds at higher structural levels to isoclinal folds with transposed bedding at deeper levels. F₁ axes are subparallel to the stretching lineation. Shear sense indicators are generally indistinct, suggesting dominantly pure shear, although top north shear is evident locally. Two mica granitoids (including the Wildrose granite which yielded a U-Pb zircon date of 89.7 +/- 2.2 Ma) are late D₁ whereas Triassic-Jurassic granitoids were fully involved in D₁ suggesting D₁ spanned a prolonged Jurassic to Late Cretaceous period. D₁ fabrics are overprinted by a younger deformation (D₂) that generated upright to moderately inclined NNW trending tight folds in S1 and an associated axial planar crenulation cleavage. These younger folds are the map scale folds described in previous studies of the area and are clearly Laramide (post ~90, pre-~60Ma) in age. F₁-F₂ superposition produces type 3 fold interference patterns at a variety of scales and raises questions on original stratigraphic calls given the layer-cake style stratigraphic interpretation in those maps. Restoration of range-tilt based on the dip of low-angle normal faults indicates the second deformation is a west-vergent Laramide age backfolding event of uncertain regional significance.