Structural Features in the Huerfano Park Area, East Flank, Sangre de Cristo Range, Colorado

Abstract

Laramide deformation along the east flank of the Sangre de Cristo Range, Colorado, has produced an imbricate thrust system with associated major folds in the Middle Pennsylvanian Minturn Formation, west of the town of Gardner. Thrusts dip 5 to 15 degrees to the west and are offset along strike by small tear faults. Major folds are inclined to overturned near the leading edges of the thrusts and become open and diminish in amplitude to the west, farther from the leading edges. Fold axes trend between N 10 Wand N 60 Wand plunge gently to the northwest or southeast. Tectonic transport was from west-southwest to east-northeast as interpreted from ma1or thrust and fold trends. Detailed analyses of minor structures such as bedding-plane thrusts, minor folds, and angle faults substantiate the style of deformation and the interpreted direction of transport Pennsylvanian sedimentary rocks were detached and thrusted, probably above a major decollement surface. Folds, bedding thrust reverse faults, and tear faults developed during thrusting and imbrication. Regionally, Precambrian rocks to the west in the Sangre de Cristo Range are interpreted to be allochthonous suggesting that the fold and thrust belt represents a zone of Laramide crustal shortening.