ANALYSIS OF LARAMIDE AND YOUNGER DEFORMATION OF A SEGMENT OF THE BIG BEND REGION, TEXAS (WRENCHING, SUPERPOSED)

Field mapping of the Sierra Del Carmen, Big Bend National Park and Black Gap Wildlife Management Area shows that the macrostructures in the exposed Cretaceous and younger rocks are persistent zones of west-northwest-oriented strike-slip faults (mainly right-lateral, some left-lateral), north-northwest-oriented monoclines, and north-northwest-oriented normal faults.;Right-lateral divergent wrenching along the west-northwest-oriented faults due to Basin-and-Range extension formed pull-apart grabens. The north-northwest-oriented faults are mainly dip-slip and bound the pull-apart grabens that also end against the west-northwest-oriented fault zones.;The west-northwest-oriented fault zones are Laramide and Basin-and-Range rejuvenation of pre-existing faults in the basement that were active during the Late Paleozoic and possibly earlier.;Landsat images show a set of right-stepped, en echelon west-northwest-oriented lineament zones in the Trans-Pecos area and the adjacent part of northern Mexico. These lineaments are a part of the Texas lineament. At the scale of the field mapping, each of these lineaments is one of the west-northwest-oriented, left-stepped, en echelon fault zones.;The west-northwest-oriented left-stepped en echelon faults occur in zones about 5.5 km (3.5 mi) apart. The monoclines decrease in structural relief toward and are bounded by these fault zones. Mesoscale structures (minor folds, contraction faults, and tectonic stylolites) and calcite twin-lamellae indicate that (sigma)(,1) was oriented N70(DEGREES)E. This Laramide compression caused left-lateral convergent wrenching which formed the north-northwest-oriented monoclines, west-northwest-oriented hinge, a few west-northwest-oriented left-lateral strike-slip faults, mesostructures, and calcite twin-lamellae.