CRETACEOUS FORELAND-BASIN DEVELOPMENT ON PREVIOUSLY RIFTED CRUST IN THE SOUTHWESTERN U.S.: FAR-FIELD RESPONSE TO GUERRERO ARC COLLISION

U-Pb zircon geochronology and biostratigraphy provide insights into a late Albian-Cenomanian Cretaceous foreland-basin system in New Mexico, recorded by the Mojado Fm. and equivalent units in N. Sonora, and the basal Dakota Fm. in NW NM, as the Western Interior seaway (WIS) encroached. These strata thin and overlie older rocks with distance from the crustal load; subjacent strata include Aptian-mid-Albian strata in the proximal foredeep, Permian strata in the distal foredeep and Proterozoic basement on the forebulge, the site of a former Late Jurassic-Aptian rift shoulder. Detrital zircons yielded max. depo. ages of the Mojado (99.1±1.7 Ma), Sarten (97.7±1.4 Ma), and Beartooth (101.5±1.6 Ma) Fms. Detritus in these units was derived primarily from the west and north. Zircon ages of ashes from the overlying Mancos Fm. in the Little Hatchets (97.2±1.6 Ma), Cookes Range (94.4±0.8 Ma), and Burro Mtns. (96.3±1.3 Ma) indicate the timing of transgression of the WIS into the foredeep and onto the forebulge. Ammonoids from basal strata of the Mancos Fm. in the Burro Mtns. identify the mid-Cenomanian Acanthoceras amphibolum zone, and overlap the dated ash bed there, so this ash is likely the x bentonite, an important regional datum. In northern NM, the fluvial Encinal Canyon Mbr. marks the base of the Dakota Fm. and records a sediment source to the north. Our zircon ages of the Encinal Canyon (99.4±1.5 Ma) and an ash (97.6±1.3 Ma) from the marine Oak Canyon Mbr. of the intertongued Dakota-Mancos indicate temporal overlap of the Encinal with the Mojado of S. NM and time-transgressive migration of the Cretaceous shoreline into the back-bulge region of N. NM by the mid-Cenomanian. Cenomanian zircons were derived from the Sierran/Peninsular arcs. Tectonic subsidence curves of the Jurassic-Cenomanian section indicate that load-induced subsidence began ~120 Ma, prior to Mojado deposition, following 40 m.y. of extensional subsidence in the Bisbee basin. We interpret renewed subsidence as a flexural response to crustal shortening caused by collision of the Guerrero arc with western Mexico and attendant development of a foreland basin. The collision therefore terminated crustal extension in the Bisbee basin in the middle Albian and initiated basement-involved shortening and rift-basin inversion that continued through the Cretaceous.