--> Abstract: Significance of Orthogonal flow in the Funeral Mountains Metamorphic Core Complex, Death Valley, California: Insights from Geochronology and Microstructural Analysis, by Katrina M. Sauer, Michael L. Wells, and Thomas D. Hoisch; #90181 (2013)

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Significance of Orthogonal flow in the Funeral Mountains Metamorphic Core Complex, Death Valley, California: Insights from Geochronology and Microstructural Analysis

Katrina M. Sauer1, Michael L. Wells1, and Thomas D. Hoisch2
1University of Nevada Las Vegas, Las Vegas, NV
2Northern Arizona University, Flagstaff, AZ

The Funeral Mountains metamorphic core complex (FMMCC) in Death Valley, California, exposes middle to lower crustal rocks of the Sevier-Laramide orogen in the footwall of the Boundary Canyon detachment (BCD). In Monarch Canyon, the structurally deepest rocks in the FMMCC record upper amphibolite facies metamorphism with migmatites developed at the deepest levels. The Monarch Spring fault (MSF) juxtaposes migmatitic paragneisses below against pelitic schists and marbles above, and represents a deformed anatectic front. In the footwall of the BCD above the MSF, distributed ductile deformation and stratigraphically-localized high-strain zones, termed intra-core shear zones, are responsible for attenuation and local stratigraphic omission during topnorthwest non-coaxial deformation. The relative contributions of Late Cretaceous-early Tertiary and Miocene extensional strains responsible for the top-northwest fabrics remains unclear, and is being addressed by ongoing thermochronologic, microstructural, and EBSD studies. Our working hypothesis is a polystage extensional history in the FMMCC, with Late Cretaceous extensional intracore shear zones locally reactivated during the Miocene. Below the MSF, migmatitic paragneisses lack the top-northwest fabrics, and instead exhibit heterogeneous strain with a northeast-trending mineral lineation and a localized, strong fabric asymmetry indicative of a top-southwest sense of shear. We propose that the anatectic front is an apparent zone of structural decoupling between top-northwest shear above and top-southwest shear below the MSF. Structural and geochronologic studies are currently underway to establish whether the orthogonally-directed flow above and below the anatectic front were coeval or developed in sequence with a progressive change in kinematics.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013