DEXTRAL TRANSPRESSIONAL DEFORMATION PRESERVED IN CRETACEOUS ARC PLUTONS OF NORTHWESTERN NEVADA

Multiple plutons in northwestern Nevada are associated with Cretaceous-aged arc magmatism. We conducted an integrated structural (anisotropy of magnetic susceptibility, microstructure, and field fabric analysis) and geochronological (U-Pb zircon geochronology) study of the Sahwave Batholith (95-88 Ma) and a pluton of the older Nightingale intrusive suite (ca. 106 Ma) to constrain the emplacement history and regional intra-arc deformation in central Nevada. The Power Line pluton – part of the Nightingale intrusive suite - contains solid-state deformation fabrics with a vertical, NNW-striking foliation and vertical lineation. These fabrics are consistent with pure shear dominated transpression observed in the western Idaho shear zone. Further, the timing of deformation is similar to the western Idaho shear zone, with significant deformation of ~106 Ma units but significantly less deformation in ~90 Ma units (e.g., the Sahwave batholith, the Fox Range, and Granite Mountain plutons). Anisotropy of Magnetic Susceptibility (AMS) studies of the Sahwave batholith (95-88 Ma) reveal more distributed shear throughout the incrementally emplaced units. Microstructural observations and AMS fabrics show predominately magmatic fabrics, with sub-horizontal lineations. However, there are also late-stage, small-scale dextral shear zones in the youngest unit. We interpret these plutons to be intruded during regional deformation, similar to other syn-emplacement shear zones in the Sierra Nevada Batholith.

The solid-state deformation fabrics in the Power Line pluton are consistent with kinematics and timing of deformation in the western Idaho shear zone. The kinematics, style (syn-emplacement), and timing of the Sahwave batholith is more consistent with deformation of the youngest magmatism (e.g., Tuolumne and Mono Pass Intrusive Suites) in the Sierra Nevada batholith. As such, we can link the deformation of middle-Late Cretaceous magmatism and deformation patterns in northwestern Nevada to regional-scale dextral transpressional and magma emplacement in the Central Cordillera.