Paper No. 116-10
Presentation Time: 10:45 AM
STRUCTURAL AND KINEMATIC HISTORY OF THE CHLORIDE CLIFF REGION: IMPLICATIONS FOR TECTONIC INHERITANCE IN THE FORMATION OF THE FUNERAL MOUNTAINS METAMORPHIC CORE COMPLEX, DEATH VALLEY, CA
In this study, we explore the role of early contractional orogenesis and its influence on the tectonic development of large-scale multi-phase extension. The Funeral Mountains metamorphic core complex (FMCC), located in Death Valley National Park, CA, has a complex history of NW extension that was predated by large-magnitude tectonic burial. Detailed structural mapping reveals that the area has a protracted history of contraction, burial, and extension, culminating with Miocene exhumation by large-magnitude top-NW extension along the Boundary Canyon detachment (BCD) fault. Burial, interpreted to be Late Jurassic based on a prior Lu-Hf garnet age (158.2 ± 2.6 Ma) from the Indian Pass area, ~ 8 km to the SE, produced a well-defined bedding-parallel foliation with local asymmetric structures showing top-SE shear including shear bands and mantled porphyroclasts in schist, and asymmetric strained clasts in diamictite of the Kingston Peak Fm. The early foliation was subsequently folded during a second contractional event (Early Cretaceous?). These folds are locally pervasive in the SE portion of the range as mesoscopic to map-scale folds that record SE-vergence. Two periods of top-NW extensional deformation overprint the earlier top-SE fabrics: Late Cretaceous(?) intracore shear zones including the Eastern shear zone and the Chloride Cliff shear zone (CSZ), and the Miocene BCD. Oligocene diabase dikes cut the CSZ, indicating the shear zone was inactive during the Miocene and most likely active during the Late Cretaceous, consistent with Late Cretaceous muscovite 40Ar/39Ar cooling ages. We hypothesize that the BCD is the final expression of a Late Jurassic thrust fault that was reactivated during the Late Cretaceous and again in the Miocene. This hypothesis also provides a mechanism for deep burial of the footwall that led to Barrovian metamorphism in the Late Jurassic, which cannot be explained from other known thrusts in the region. Understanding the geometric and kinematic relationships between early-stage contraction and later extension has important implications for the genesis and evolution of the FMCC, metamorphic core complexes worldwide, detachment faulting, and the influence of reactivation on the rheology of the crust.