The pre-Tertiary geology, structural evolution, and geochronology of the Pueblo Mountains, Nevada-Oregon

The pre-Tertiary rocks of the Pueblo Mountains are a series of volcanic and volcanogenic rocks intruded by Middle Jurassic and possibly younger plutons. The entire sequence has undergone sub-greenschist to greenschist facies metamorphism. The Pueblo Mountains can be divided into two zones: (1) a northeast-trending, southeast-dipping shear zone in the southeast; and (2) an undeformed zone in the northwest. Three phases of deformation are associated with and restricted to the shear zone, and all show top-to-the-NW sense of shear. $\sp{40}$Ar/$\sp{39}$Ar geochronology for biotite from within the shear zone produces a minimum age for D$\sb1$ of 95 Ma. The Pueblo Mountains shear zone may be related to a similar middle Cretaceous structure in the northern Pine Forest Range, and is also similar to structures developed during and after the poorly understood suturing of the Blue Mountains province to the North American craton