LATE CRETACEOUS MAGMATISM AND UPLIFTS IN SOUTHWEST NEW MEXICO: FARALLON TEAR RIPS THROUGH NEW MEXICO?

Late Cretaceous uplifts and intermontane basins in the southern U.S. Cordillera—a region defined as south of the Colorado Plateau and Mogollon-Datil volcanic field—consist of narrow basement-cored structures that resemble those of the central Rocky Mountains. However, a few salient differences exist, and include, (1) uplift-to-basin structural wavelengths which are ~50% smaller than contemporaneous Laramide structures in central Wyoming; (2) the occurrence of volcanic and magmatic centers within Late Cretaceous basins; and (3) development of basement-involved structures inboard of the active Tarahumara volcanic arc. The Late Cretaceous Tarahumara arc in Sonora, Mexico, is defined as a northwest-southeast arc that paralleled the Farallon paleo-trench. However, contemporaneous to this volcanic arc are a series of coeval magmatic centers along an approximate northeast-southwest belt through southwest New Mexico which do not systematically young to the northeast. This northeast-southwest magmatic belt occupies a region that likely represents the approximate margin between flat-slab subduction and normal subduction to the south. Could Late Cretaceous magmatism in southwest New Mexico represent localized magmatism along the southeast margin of the classic Laramide flat-slab corridor, possibly at a tear in the subducting Farallon plate or along the margins of a subducted oceanic plateau? If so, southwest New Mexico would represent a unique segment of the Laramide orogenic belt where basement-involved structures coexisted with magmatic centers at the southern margin of the flat-slab corridor.