MID-CRETACEOUS DEFORMATION IN THE MAGMATIC ARC OF NORTHWESTERN NEVADA

We provide evidence for a ~100 Ma deformational event in northwestern Nevada, constrained by granitic rocks of the Nightingale intrusive suite. The Nightingale intrusive suite lies between the Sierra Nevada batholith of California and the Idaho batholith. The 106 Ma Power Line pluton – part of the Nightingale intrusive suite – records a penetrative ductile shearing fabric. In general, the Power Line pluton contains solid-state fabrics with a vertical, NNW-striking foliation and vertical lineation. Dextral shear sense is observed on faces perpendicular to the lineation direction, consistent with an interpretation of pure shear dominated transpression. We present integrated structural data (anisotropy of magnetic susceptibility, microstructure, and field fabric analysis) that characterize these fabrics and U-Pb zircon geochronology to constrain the timing of deformation. While the 106 Ma Power Line pluton contains solid-state fabrics, the younger, Late Cretaceous plutons of the Sahwave batholith (94-88 Ma) do not. Thus, we constrain deformation to have occurred between 106 and 94 Ma. We note that these fabrics are consistent with the kinematics (pure shear dominated transpression) and timing (~100 Ma) of deformation in the western Idaho shear zone, located to the north. We attribute this deformation to a widespread, ~100 Ma dextral transpressional event which affected the magmatic arcs along the U.S. portion of the North American margin.