LATE PALEOZOIC STRUCTURES IN THE ANCESTRAL ROCKY MOUNTAINS OF THE WEST TEXAS AREA - PRODUCT OF NORTHEAST-DIRECTED COMPRESSION

The segment of the Ancestral Rocky Mountains (ARM) that extends south through New Mexico into Texas contains small to medium basement-cored uplifts, folds, thrust faults and strike-slip faults. Although block motions were likely complex, the pattern of the features is consistent with SW-NE compression, both in early (Atokan) and late (Wolfcampian) time. Major left-lateral faults strike WNW to W; possible right-lateral faults occur on northerly trends. The largest thrust fault known in the basin, on the southwestern flank of the Fort Stockton Uplift, is SW-vergent, and faces the deepest part of the Delaware Basin. This direction of compression is similar to that observed in the southern Oklahoma segment of the ARM (Wichita Uplift NE-vergent overthrust, left-lateral faulting). It may also be consistent with ARM block geometries in New Mexico, formed in transpressive strike-slip, and in Colorado.

A NE-SW maximum compressive stress is grossly inconsistent with the Ouachita-Marathon thrust belt to the southeast, which was being thrust northwestward onto the craton during the same time. The ARM-generating stress may have originated either from the Pacific side (by flat subduction) or from strong continental collision in the Appalachian Orogen. In either scenario, lines of weakness generated either during the Proterozoic or during Cryogenian-Cambrian rifting served to concentrate stress and create the complex ARM structures.