Late Cretaceous‐Early Paleogene Extensional Ancestry of the Harcuvar and Buckskin‐Rawhide Metamorphic Core Complexes, Western Arizona

Metamorphic core complexes in the western North American Cordillera are commonly interpreted as the result of a single phase of large‐magnitude extension during the middle to late Cenozoic. We present evidence that mylonitic shear zones in the Harcuvar and Buckskin‐Rawhide core complexes in west‐central Arizona also accommodated an earlier phase of extension during the Late Cretaceous to early Paleocene. Microstructural data indicate substantial top‐NE mylonitization occurred at amphibolite‐facies, and 40Ar/39Ar thermochronology documents post‐tectonic footwall cooling to