DUCTILE DEFORMATIONAL HISTORY OF THE CENTRAL PANAMINT MOUNTAINS, DEATH VALLEY, CA

The central Panamint Mountains display contractional structures related to ductile deformation event, D_1-2 analogous to overprinting seen by Hodges, et al. (1987) in the Northern Panamint Mountains. The two early, layer-parallel cleavages S_1a-1 are associated with outcrop scale isoclinal folds and a prominent NS trending stretching lineation. New U-Pb geochronology from a plutonic sheet that is fully involved in the ductile deformation indicates D₁ is no older than 178.5 ± 1.6 Ma, and is no younger than 89.6 ± 2.2 Ma based on cross-cutting plutons that are late-tectonic to these main fabrics. Finite strains associated with this fabric are variable, and where measured, show predominantly plane strain to constrictional strain consistent with the LS fabric. Strain magnitudes are consistent with shear strains between 2 and 5. Strain appears to be concentrated in carbonate units that lack strain markers indicating that these strain estimates are likely minima; however, boudinage in some carbonate units indicate stretch parallel to lineation as large as 6.5. Shear sense indicators are difficult to interpret in most of these rocks because of fabric overprints. Fortunately, asymmetric boudins in marbles and fabric asymmetries in metaplutonic rocks show a consistent top north shear sense, or dextral shear if the fabrics are restored to their pre-extensional geometry. The main fabric is overprinted by D₂, a younger crenulation cleavage that is axial planar to tight, upright folds in S₂ foliation. This overprinting fabric is demonstrably post-89 Ma, but pre-~50 Ma based on the published cooling ages, thus, we conclude these folds are Laramide age structures.