Structure and petrology of Cochetopa pluton and its metamorphic wallrocks, Saguache County, Colorado

The Cochetopa Granite pluton and its metamorphic wallrocks are exposed in an erosional window that has been cut through the Jurassic Junction Creek Sandstone (fig. 1). The area described in this paper is bisected by northward-flowing Cochetopa Creek and includes approximately 33.7 km². Cochetopa Granite pluton includes about 14.5 km² and the metamorphic wallrocks the remainder. Nine different lithologically distinct mappable units are present as well as dikes of pegmatite and aplite.

 

The major lithologic units are granite-gneiss (ggn), porphyroblastic gneiss (Pgn), quartzite (qz), metadiorite (mdi), mixed zones (mz, and mz,), metagabbro (mg), Cochetopa Granite (Cg), and Coche-topa granite-gneiss (Cgn). Figure 2 shows the units in geological cross section.