The Mesozoic and Tertiary tectonics of the Panamint Range and Quail Mountains, California

The southwestern portion of the Basin and Range province preserves polyphase Mesozoic and Tertiary deformation. Examination and determination of these deformations and their tectonic history is crucial not only to the understanding of the regional tectonic evolution, but also to the understanding of basic tectonic processes. The three chapters presented in this dissertation examine different aspects of the deformation in this region.; The Panamint Range is preserves a relatively complete record of the deformation due to Mesozoic tectonism in the southwestern Cordillera: D1 is east-vergent contraction between 175 and 148 Ma; D₂ is an episode of dike emplacement at ∼148 Ma; D₃ is intrusion-related folding of the margin of the Manly Peak batholith at ∼146 Ma; D₄ is top-eastward contraction at ∼75 Ma; D₅ is west-vergent extension at ∼72 Ma; and D₆ is dextral arc-parallel at ∼60 Ma. The Panamint Range tectonic history is unique because the deformation is relatively well constrained in time and crosscutting relationships exist between the different deformations. These data thus show that contractional deformation was not synchronous with extensional deformation in the southwestern Cordillera. This history fits with a tectonic history compiled for the southwestern Cordillera, except for the ∼60 Ma dextral shear of the Panamint Range, which occurs at 80–90 Ma in the other localities of the southwestern Cordillera. This tectonic history for the southwestern Cordillera shows a first order relationship between the direction and magnitude of relative plate convergence vectors for the North American-Pacific Ocean plates. Regional ∼72 Ma extension does not fit this simple relationship; it occurs during a moderate rate of convergence, immediately after a period of very rapid convergence and resultant building of high topography, as in critical taper models of orogenic belts.; The western Quail Mountains expose the intersection of two strike slip faults that accommodate a large amount of the Tertiary age transtensional strain of this region: the dextral Panamint Valley and the sinistral Garlock faults. The western Quail Mountains consist of three crustal blocks that were juxtaposed by the movement of these faults. The correlations of the original position of these crustal blocks and the history of brittle fabrics in the western Quail Mountains yields a model of the tectonic evolution of the intersection of the Garlock and Panamint Valley fault zones. The dextral motion on Panamint Valley fault zone is taken up at its southern end by drag folding along the Garlock fault, and then crustal slices of the southern end of the Panamint Valley fault are incorporated onto the Garlock fault zone. The result of this interaction is a zone along the north side of Garlock fault zone of crustal slices from the eastern side of the Slate Range.; A Tertiary-age extensional duplex is present along the western flank Panamint Range. This duplex is a remnant of the hanging wall that was added to the footwall and therefore preserves information about the processes of the large magnitude extensional faulting. Mesozoic age structural highs and lows in the footwall act as asperities to the extensional faulting, the creation of the duplex effectively fills in the structural lows. Observations of the duplex show that the duplex deformation was non-coaxial, thus the duplex deformation not only accommodated east-west tension, but also accommodated a portion of north-south compression.