CARBONATE UNITS IN SURPRISE CANYON – A KEY TO UNDERSTANDING THE TECTONIC PAST OF THE PANAMINT MOUNTAINS

The central Panamint Mountains display contractional structures related to ductile deformation with two early, layer parallel cleavages associated with outcrop scale isoclinal folds and a prominent NS trending stretching lineation. These structures developed during the Mesozoic and are overprinted by a younger, post-80Ma, crenulation cleavage that is axial planar to tight, upright folds in foliation. These complex structures are well exposed in lower and middle Surprise Canyon where different marble bands have been correlated to three Neoproterozoic units: the Crystal Spring Formation and the Beck Spring Dolomite of the Pahrump Group, and the Noonday Formation. The studies that made these conclusions did not recognize the two earlier phases of deformation that produced the bulk of the finite strain, raising questions. To evaluate the correlations we exploited the distinctive δ¹³C values of carbonate units known from unmetamorphosed equivalents in the eastern Death Valley region and compared them with our new data from marble units in the Panamint Mountains. The study was further aided by detailed mapping that combining 2D digital mapping with local, detailed 3D mapping on a high-resolution terrain model generated from both Terrestrial LiDAR and ground-based photogrammetry. The geochemical data was used to refine the correlation of units, which now differentiates the marble mass into the three oldest formations of the Pahrump Group: the Crystal Spring Formation, the recently defined Horse Thief Spring Formation, and the Beck Spring Dolomite. Our mapping demonstrates that large finite strains are present in these units both in terms of observed object strains and dramatic variations in unit thicknesses related to deformation. We suspect large-scale isoclinal fold systems are present, but such features are only observed in lower Surprise Canyon. Deformation of the 80Ma pluton that intruded the crystalline basement exposed in central Surprise Canyon suggests the youngest deformation is Laramide in age.