Late Triassic Texas uplift preceding Jurassic opening of the Gulf of Mexico: Evidence from U-Pb ages of detrital zircons

Abstract

We use U-Pb ages for 2655 individual detrital zircon grains in 30 samples of Upper Triassic (Carnian‐Norian) sandstones of the southwestern USA (our data) and northern Mexico (other data) to infer regional Late Triassic provenance relations and tectonic features, which included a prerift uplift in Texas precursory to Jurassic opening of the Gulf of Mexico. Detrital zircons in sandstones from central paleorivers of the Chinle-Dockum fl uvial system on the High Plains (USA) and Colorado Plateau, and from the marine terminus of the fl uvial system along the eastern fl ank of the Auld Lang Syne backarc basin in the Great Basin, refl ect regional dispersal of sediment from the Ouachita orogen and adjacent Mesoproterozoic basement exposed on the northern fl ank of the rift uplift. The composite grain population of Ouachita-derived sands displays dominant U-Pb age peaks at 1100‐1050 Ma (Grenvillian) and subordinate Neoproterozoic (630‐550 Ma) and Paleozoic (475‐400 Ma) age peaks inferred to document recycling of sand grains from the Ouachita system. The Ouachita detritus was supplemented by contributions from Mesoproterozoic basement rocks of southwest Laurentia (compound 1805‐1655 Ma and unitary 1440 Ma age peaks) and from Permian‐Triassic arc assemblages of northeastern Mexico (composite 285‐215 Ma age peak). Master Chinle-Dockum paleodrainages extended east-southeast‐west-northwest for 2000 km from Texas to Nevada, fl owing along the axis of a backarc trough formed by dynamic subsidence behind the Cordilleran magmatic arc, from headwaters in the Texas prerift uplift to the sediment trap of the backarc marine basin where the Auld Lang Syne Group accumulated. Sandstones from peripheries of the linked fl uvial and marine depositional systems contain contrasting populations of detrital zircons derived either from the relict Amarillo-Wichita uplift, which fed abundant Cambrian zircons derived from an uplifted aulacogen-fl oor igneous assemblage, to selected basal units of the fl uvial system, or from the Cordilleran arc assemblage to the south and west. The youngest Dockum sample from the Ouachita foreland on the High Plains contains abundant Devonian zircons probably derived from the Ouachita metamorphic core zone now present only in the Texas subsurface. Sandstones along the southern fl ank of the Chinle backarc basin on the southern Colorado Plateau contain populations of detrital zircons similar to those in sandstones of the AntimonioBarranca forearc basin (Sonora) that was farther south beyond the arc axis. Sediment transported longitudinally from the Texas uplift to the El Alamar paleoriver and Potosi subsea fan of northeastern Mexico contains populations of detrital zircons similar but not identical to those in Chinle-Dockum fl uvial strata of the High Plains shed transversely from the rift uplift.