New Mexico Geological Society Annual Spring Meeting — Abstracts

New geochronological, structural, and sedimentological data provide insight into the complex deformational, erosional, and magmatic history of the Little Hatchet Mountains. Previous studies in the range proposed that an array of north-east verging basementinvolved structures and NW-, NE-, and east-west trending normal and strike-slip faults are related to two distinct stages of Laramide deformation, that include: (1) a block uplift stage beginning in the Late Cretaceous followed by (2) left-lateral wrenching between the Paleocene and Eocene. Reinterpretation of mapped relationships with additional data suggests that Laramide orogenesis, as seen in the Little Hatchet Mountains, cannot be clearly segregated into two discrete deformational periods of variable style. Instead, Laramide structures include low- and high-angle thrust faults that generally verge to the northeast, involve basement (1080.4 ± 6.8 Ma; U-Pb zircon), and represent reactivated Bisbee rift faults. Faults with N60E, N60W, and E-W trends and latitic intrusions all formed as a response to a north-south extension event that occurred in the Oligocene, as suggested by the age of a granitic sliver (33.1 ± 1.4 Ma; U-Pb zircon) along an east-west normal fault with at least 1000m of throw. Subsequent Neogene Basin and Range normal faults created several offset blocks in the range and juxtaposed variable structural depths from the two earlier deformational events. New interpretations and field relationships should be considered for future geophysical and tectonic studies regarding the subsurface structure and kinematic histories of the surrounding area and ranges.