Evidence for Pennsylvanian transpression from preliminary kinematic fault analysis in the Sacramento Mountains, New Mexico
Abby W. Howell, Eric A. Erslev, and Steven M. Cather
Folds and faults in the western Sacramento Mountains are unconformably overlain by undeformed or weakly-deformed Permian strata, offering an excellent opportunity to study Pennsylvanian deformation related to Ancestral Rocky Mountains tectonics. Three major Pennsylvanian-Early Permian, north-south-striking faults in the range were chosen for detailed field study and kinematic analysis: the Fresnal, Alamo and Bug Scuffle faults. The faults studied here have been interpreted as either normal (Pray, 1959, 1961), vertical (Johnson, 1985), arid, in the case of the Fresnal fault, normal with a dextral component (Cather, 2000) due to the obliquity of the fault with local fold axes. Slickensided minor faults (n = 588) were measured on and adjacent to these major faults. Eigenvector analysis of the slickenlines gives an average slip orientation of S72°W-37°. This average slip trend is 18 degrees from perpendicularity with the average fault strike, suggesting dextral oblique motion. Slickenlines measured on the major fault planes themselves (n = 56) are bimodal, with near vertical and near horizontal orientations. This indicates that both strike-slip and dip-slip motion occurred on the faults, perhaps in two separate events or during a partitioned transpressional event. These possibilities are being tested by more thorough kinematic analyses of fault and fracture data, construction of structural cross-sections and 3D models.
- Howell, Abby W.; Erslev, Eric A.; Cather, Steven M., 2002, Evidence for Pennsylvanian transpression from preliminary kinematic fault analysis in the Sacramento Mountains, New Mexico, in: Geology of White Sands, Lueth, Virgil W.; Giles, Katherine A.; Lucas, Spencer G.; Kues, Barry S.; Myers, Robert; Ulmer, Scholle, Dana S., New Mexico Geological Society, Guidebook, 53rd Field Conference, pp. 103-106.