LARGE-DISPLACEMENT LARAMIDE THRUSTING IN THE SANGRE DE CRISTO RANGE, COLORADO

The Sangre de Cristo Range north and east of the Great Sand Dunes is composed of thrust plates that have moved many kilometers east. Large horizontal displacement is indicated by 1) thrust plates of older rocks that extend over younger rocks at least 10 km across the range, 2) windows of Paleozoic rocks beneath Proterozoic rocks, and 3) contrasting stratigraphy in adjacent plates.

The Sand Creek plate consists of Proterozoic gneiss and granitic rocks overlain by the Crestone Conglomerate Member of the Pennsylvanian and Permian Sangre de Cristo Formation. Crestone Conglomerate was deposited directly on Proterozoic rocks far to the west, on the flanks of the late Paleozoic Uncompahgre highland. In contrast, the lower plate consists of thick Pennsylvanian Minturn Formation and Sangre de Cristo Formation, deposited in the central Colorado trough.

The Deadman Creek plate consists of Proterozoic gneiss and is contiguous with the Sand Creek plate. The Deadman Creek thrust and its lower plate is exposed only in a window on the west side of the range. In the window, Proterozoic gneiss and granitic rocks are overlain by Ordovician Harding Formation through basal Minturn Formation, originally deposited in the central Colorado trough. These rocks are now exposed 5-10 km southwest of the Crestone Conglomerate of the Sand Creek plate, illustrating extreme telescoping of contrasting stratigraphic sections.

The Mosca Creek plate consists of Proterozoic gneiss and granitic rocks. It was probably exposed to erosion during Paleocene time and is the likely source of arkose in the northwestern Raton basin. The lower plate consists of Proterozoic gneiss overlain by lower Minturn Formation, deposited in the central Colorado trough. Along Mosca Creek, the thrust and its lower plate are exposed in a window that extends 5 km across the range. East of Blanca Peak, a second window extends the minimum displacement to 10 km.