Transpressional shearing and strike‐slip partitioning in the Late Cretaceous Sierra Nevada magmatic arc, California

The Rosy Finch shear zone (RFSZ) represents an example of synmagmatic, strike‐slip tectonics in the east central Sierra Nevada and provides information on transpressional tectonics within magmatic arcs. The RFSZ (1–4 km wide and 80 km long) is contained in Late Cretaceous granitoids (92–83 Ma) of the Mono Pass Intrusive Suite. Dextral strike‐slip deformation is indicated by a continuous band of orthogneiss, mylonitic, and cataclastic deformation, characterized by subvertical foliations with subhorizontal lineations. The style of dextral shearing in the Rosy Finch shear varies along strike, from wide zones of ductile deformation in the youngest plutons to narrow zones of cataclastic deformation in the older plutons. Deformation of the youngest granitoids is synmagmatic, as constrained by both field observations and isotopic studies. Dextral shearing occurs concurrently in contemporaneous Intrusive Suites to the north and south (Tuolumne and Mount Whitney) suggesting strike‐slip movement along the axis of active plutonism. Field studies also suggest that contraction across the arc acted concurrently with strike‐slip movement, consistent with a transpressional setting for the Late Cretaceous Sierra Nevada magmatic arc. Comparison of the field data with strain models of oblique plate convergence suggests that the RFSZ is a preserved ductile signature of transcurrent motion of strike‐slip partitioning within a transpressional orogenic system. Recent plate reconstructions indicate a switch from sinistral to dextral oblique convergence at ∼95 Ma, which is consistent with the timing constraints on the dextral movement on the RFSZ.