SOUTHERN LARAMIDE DEFORMATION TIMING (ARIZONA-NEW MEXICO) CONSTRAINED BY INTEGRATED GEOLOGY AND THERMOCHRONOLOGY: IMPLICATIONS FOR CRETACEOUS-PALEOGENE TECTONIC PROCESSES

The southern Cordilleran transect has been used as a classic example of Cretaceous-Paleogene west-to-east sweeping magmatism and deformation due to shallowing subduction of the Farallon slab. An integrated thermochronologic and geologic transect of Laramide deformation timing from Gold Butte (Nevada) to Raton basin (New Mexico) suggests a more complex Laramide deformation history. Low-temperature apatite fission track and apatite (U-Th)/He thermochronology data were modeled (together where possible) in the program HeFTy to produce continuous time-temperature (t-T) path models. Geologic data is from pairing the stratigraphic and geologic records of Laramide basins to the geologic and thermochronologic data of an associated arch (e.g., San Juan basin/Nacimiento arch). These arch-basin pairs allow for independent timing constraints and refined t-T path models. Deformation criteria (onset, duration, rate, and cessation of deformation) are then estimated from an automated script for all “good” t-T paths from each HeFTy model. This allows for a comprehensive look at not only when deformation began, but also characterizes how it evolved throughout the orogen. Results show that from west to east, onset of rapid cooling was ~90 Ma in the west (Gold Butte and western Grand Canyon), 65-72 Ma in western New Mexico (Zuni range), ~80 Ma in central New Mexico (Nacimiento range), and 65-70 Ma in the southern Rocky Mountains (Sangre de Cristo range). In the west (Grand Canyon) and east (Manzano range and San Juan basin), cooling and sedimentation pulses at ~70 and ~50 Ma suggest progressive contraction into the middle Eocene. Thus, it appears that contraction onset swept ~90-70 Ma across the southern foreland, though evidence suggests continued episodic cooling over a protracted period (90-45 Ma). The early onset across the foreland, protracted history, and complex deformation pattern are perhaps difficult to explain with models of simple slab shallowing or the conjugate Shatsky rise, and suggest influence of crustal anisotropy, variable slab devolatilization, and/or contributions from other tectonic sources at the evolving plate margin. In combination with similar work in the northern Rocky Mountains, this timing synthesis will constrain likely tectonic processes responsible for Laramide deformation.