A DETRITAL ZIRCON RECORD OF THE PROTEROZOIC TO CENOZOIC TECTONIC GROWTH OF THE SOUTHERN MARGIN OF NORTH AMERICA, TRANS-PECOS REGION, WEST TEXAS

The Appalachian and Cordilleran orogenic belts of North America and their related sedimentary basins intersect in the Trans-Pecos region of west Texas. The well exposed Proterozoic to Cenozoic strata in this area archive a long-term record of tectonic and sedimentary processes along the southern continental margin. Results from 3,981 new U-Pb ages from detrital zircons and new field data allow for the following interpretations. The oldest Proterozoic strata in the Trans-Pecos region were locally sourced from the Southern Granite Rhyolite and Yavapai basement provinces. An influx of 1300 – 900 Ma detrital zircons in late Proterozoic to Cambrian strata reflect the growth and erosion of the Grenville orogenic belt along the southern margin of North America. The introduction of 600 – 400 Ma detrital zircons in Late Paleozoic submarine fan strata are interpreted as being recycled from primary Appalachian plutonic sources and represent a regional switch to eastern North American sources of sediment. These submarine fan strata were incorporated into an accretionary prism/thrust belt along the continent-to-continent suture zone between Gondwana and Laurentia. The broad distribution of Precambrian detrital zircons in these samples is interpreted to be a product of recycling of multiple basement and sedimentary sources along the suture represented by the Allegheny-Ouachita-Marathon orogenic belt. An introduction of 245 – 75 Ma zircons in Upper Cretaceous to Paleogene strata record three main pulses of Cordilleran magmatic arc and foreland basin development, and a regional switch to western North American sources of sediment. Neogene tectonic reconfiguration of the Trans-Pecos region is reflected in the detrital zircon populations of the modern Rio Grande River. This river is characterized by an introduction of 50 – 20 Ma detrital zircons that are a product of Eocene and Oligocene ignimbrite flare-ups associated with Farallon slab rollback and Basin and Range volcanism. The introduction of large volumes of Cenozoic igneous rocks to extensional landscapes in the Trans-Pecos region profoundly altered topography, fluvial drainage systems, and sediment routing along the southern continental margin of North America.