New Mexico Geological Society Annual Spring Meeting — Abstracts

Models of Laramide orogenesis in New Mexico and southern Colorado fall into two categories: models that involve east-vergent reverse faults, and models that include both right-lateral strike-slip and east-vergent reverse faults, in which strike-slip motion was imparted by northeast translation of the Colorado Plateau, The Montosa fault, a 100km northeast-trending fault which bisects the Los Pinos and the Manzano Mountains of central New Mexico, has been interpreted as a Laramide (Late Cretaceous-early Tertiary) age structure. As with other Laramide faults in New Mexico, the sense of movement along the Montosa fault is controversial. Structures and kinematic indicators along the Montosa fault, including slickenlines, Riedel shear fractures, and extension fractures are currently being studied to constrain fault kinematics. Fission track analyses of rocks from both sides of the fault will be used to determine the age of denudation of the hanging wall and footwall and constrain the magnitude of vertical displacement. Preliminary results suggest both reverse and right-lateral strike-slip motion across the fault. Different models of Laramide deformation in New Mexico will be critically evaluated based on preliminary fission track and structural data.