NEW GEO- AND THERMOCHRONOMETRIC CONSTRAINTS OF THE DEVIL’S RIVER UPLIFT AND INSIGHTS INTO THE LATE PROTEROZOIC AND PALEOZOIC EVOLUTION OF THE SOUTHERN MARGIN OF NORTH AMERICA

Exposures of the Neoproterozoic to early Paleozoic continental margin, following the Rodinia rifting, are rare or often ambiguous in their nature or tectonic affinity in the southern and southwestern United States. The Devil’s River uplift located in southwest Texas represents one of these crustal blocks that has been interpreted to be part of the rifted late Proterozoic/Cambrian margin that was subsequently thrust northward as an autochthonous basement block during the Ouachita orogeny. It was cored by a legacy well (Shell No. 1) that reached a total depth of 9693 feet and penetrated both gneissic and metavolcanic basement rock, as well as overlaying Cambrian metasediments, Ordovician dolomite, and Cretaceous limestone. Earlier work by Nicholas and Rozendal (1975) analyzed the basement samples from this core using K-Ar and Rb-Sr geochronology to investigate the tectonic evolution and crustal affinity of the Devil’s River uplift. Their results showed K-Ar age of 345 ± 17 Ma from a depth of 8000 ft, while Rb-Sr ages from the same depth gave an age 1121 ± 244 Ma. Results that we interpret to reflect both the original provenance as well as inversion during the Ouachita orogeny.

The aim of this study is to more clearly resolve 1) the tectonic affinity of the basement, 2) the age of the volcanic intrusive and extrusive units, and 3) the provenance of the early Paleozoic siliciclastic units, interpreted to be of North American origin. To do this, thirteen core samples from Shell No. 1, twelve of which are basement block core samples, and one Cambrian metasediment, will be analyzed using zircon U-Pb geochronology.