Early Contractional History of the Funeral Mountains and its Influence on the Formation of the Funeral Mountains Metamorphic Core Complex, Death Valley, CA

Zones of localized crustal thickening in orogenic belts commonly host low-angle normal faults, which have been controversial since their recognition. The metamorphic core complexes of the Sevier hinterland are localized within a belt that is attributed with the highest degrees of crustal thickening during Sevier orogenesis. This association of deep-rooted detachment faulting and early contractional deformation indicates an important link between the two processes, however repeated tectonic episodes often overprint and obscure the earlier fabrics, making this link difficult to study. The Funeral Mountains metamorphic core complex, located in Death Valley, CA, has a complex history of protracted SE-contraction and tectonic burial of Late Jurassic age that has since been overprinting by two periods of NW-directed detachment faulting during Late Cretaceous and Miocene time. Exposure of a Barrovian-style metamorphic field gradient and a thick stratigraphic section with large rheologic contrasts has provided a unique opportunity to investigate the apparent genetic link between contractional structures and the development of low-angle normal faults. Detailed mapping at 1:10000 scale has revealed evidence of four separate fabric forming events. Evidence for early burial was found within the Kingston Peak diamictite, which contains a well-developed bedding-parallel foliation with asymmetric strained clasts with SE-vergence. This early foliation was subsequently folded during a second period of contraction of Early Cretaceous(?) age. This event produced NNE-SSW mesoscopic to map-scale folds with SE-vergence. A new U-Pb zircon age of 95.63 ± 0.95 Ma, from a peraluminous granite intrusion that preserves no contractional fabrics, may provide lower constraints on the age of contraction. Two periods of top-NW shear overprint the earlier top-SE fabrics during the Late Cretaceous and Miocene, which produced two intracore shear zones, the Monarch Canyon shear zone and the Eastern shear zone, and the primary dome forming fault, the Boundary Canyon Detachment fault. The contractional fabrics are subparallel with extensional structures of opposite kinematics, indicating deformation generated by structures of similar orientations. These observations, in conjunction with the absence of an enigmatic thrust fault responsible for the deep burial of the Funeral Mountains, has led us to hypothesize that tectonic reactivation of a Late Jurassic thrust fault was the primary mechanism behind detachment faulting within this complex