A NEW PALINSPASTIC RECONSTRUCTION OF NEOGENE TRANSTENSION ACROSS PANAMINT VALLEY, CALIFORNIA: IMPLICATIONS FOR MESOZOIC DEFORMATION IN THE CENTRAL BASIN AND RANGE

The Panamint Valley region is often cited as accommodating a significant portion of the total Late Cenozoic strain across the Central Basin and Range. The amount of this strain is however not well known, because there are no published reconstructions using direct evidence from Panamint Valley. Published reconstructions have calculated strain by making a circuit of strain without direct correlation of rocks or structures on either side of Panamint Valley: calculating 30 to 60 kilometers of transtension across Panamint Valley.

New geologic and geochronologic data for Miocene strata and structures finds a reconstruction marker in Panamint Valley. This reconstruction marker is a package of conglomerates and monolithologic breccias which are interbedded with ~14 Ma basalt and overlain by ~13.4 Ma andesite. These sediments occur in the hanging wall of the Panamint detachment fault, but have a unique source area which exists only at one location in the footwall Panamint Range block. The total displacement recorded by this package of Miocene sediments is ~17 km.

The mismatch of displacement vectors between this new marker and previously published reconstructions is a function of the direct correlation and Miocene age of the new marker. The previously published displacements are based on a combination of Late Paleozoic, Mesozoic and Cenozoic markers. The discrepancy may be due to an unaccounted for deformation event that occurred between the time of the Paleozoic or Mesozoic thrust faulting used in the previous studies and the Miocene extension of Panamint Valley. The displacement discrepancy across Panamint Valley could be equal to the displacement of this unaccounted deformation.

One critical constraint used in the published reconstructions of Panamint Valley is extension on the Harrisburg-Tucki Mountain fault (HTMF) system. The displacement vector of this structure is compatible with the ‘missing' displacement across Panamint Valley. The HTMF system is unique in the Panamint Valley region in having ductile deformation fabrics; other Neogene detachment faults in this region have brittle fabrics. Deformation on the HTMF occurred between 100 and 11 Ma, thus the HTMF could be Late Cretaceous and could account for a pre-Neogene strain across Panamint Valley.