SEDIMENT DISPERSAL TO THE LATE CRETACEOUS-PALEOGENE MEXICAN BROKEN FORELAND FROM DETRITAL ZIRCON U-PB GEOCHRONOLOGY

Late Cretaceous-Paleogene inversion of the Jurassic-Early Cretaceous Chihuahua and Sabinas extensional basins in NE Mexico segmented the Mexican foreland into two sediment-routing systems: the Parras-La Popa routing system between the Mexican fold-thrust belt and the inverted Border Rift belt and a paleo-Rio Grande routing system north of the inverted Border Rift belt. The paleo-Rio Grande routing system navigated evolving orogenic topography in N Mexico and the SW USA Laramide province to deliver sediment to S Texas/NE Mexico. We combine detrital zircon (DZ) U-Pb data from Upper Cretaceous-Eocene strata from W Texas (Big Bend National Park) and S Texas (Eagle Pass to Laredo) along an up-to-down-dip source-to-sink depositional profile to investigate sediment dispersal, the interplay between axial and transverse sediment input, and regional drainage segregation during peripheral Laramide/Mexican orogenesis and inversion tectonics.

Depth-profiled DZ U-Pb analyses yielded dominant <85 Ma age modes that derive from Laramide and younger magmatism and 180-85 Ma age modes from various Cordilleran arcs. DZ age spectra also display subordinate Permian (Big Bend only), early Paleozoic, Neoproterozoic, 1250-950 Ma, and 1.8-1.4 Ga (more prominent in S Texas) age modes. DZ spectra also display 180-140 Ma—85-60 Ma and 1.8-1.4 Ga—85-60 Ma core-rim pairs consistent with Laramide magmas intruding the Nazas arc and Yavapai-Mazatzal crust, whereas 1.2-0.9 Ga—650-380 Ma core-rim pairs were originally sourced from the Coahuila block of north-central Mexico and subsequently recycled out of the inverted N Mexico Border rift basins.

Depth-profiled DZ U-Pb data demonstrate that W and S Texas strata were derived from Laramide magmatic provinces, Cordilleran arc sources, recycled sedimentary sources in the inverted Border Rift (Chihuahua and Sabinas Basins), and Laramide basement block uplifts. Importantly, they lack DZ ages derived from the Early Cretaceous Alisitos arc, which argues against sediment derivation from W Mexico and input via the Parras-La Popa routing system. These data demonstrate that the inversion of the Chihuahua-Sabinas basins segregated the paleo-Rio Grande system from the Mexican foreland, while both inputting sediment transversely and guiding sediment axially to S Texas and the NW Gulf of Mexico.