Casey, John F.2014-07-242014-07-24May 20142014-05http://hdl.handle.net/10657/712This study refines regional differences in the cessation of Laramide compressional deformation and the subsequent initiation of episodic slab-asthenosphere influenced ignimbrite-rhyolite volcanism in West Texas by utilizing LA-ICP-MS U-Pb zircon geochronology. Ages have been obtained for volcanic rock samples that occur both above and below the angular unconformity demarcating compressional deformation structures below and a lack of contractional structures above, as well as the maximum depositional ages for Tertiary siliciclastic formations present below the unconformity. By assessing the provenance of the detritus age-spectra from the siliciclastic formations the eastward migration of the magmatic arc, subsequent uplift, and arrival of the flat-slab to the Texas-New Mexico border (~47 Ma) and beyond has been tracked by assessing the increasing abundances more proximal detritus in each progressively younger formation. The volcanic results suggest cessation of shortening associated with Laramide-style deformation and uplift in the northern Trans-Pecos region occurred by ~38-36.5 Ma (Eocene), but persisted in the south e.g., in the Big Bend National Park region until ~31 Ma (Oligocene). Pre-Basin and Range Tertiary volcanism and compressional deformation associated with the Laramide orogeny in the Trans-Pecos region of West Texas is attributed to: 1) the subduction of thick, buoyant oceanic crust on the Farallon slab causing a major slab flattening period that resulted in magmatic arc volcanic activity progressively migrating eastward to Trans-Pecos Texas; 2) Laramide compression, uplift, and accelerated erosion directly preceding or synchronous with arrival of the flat-slab; 3) a quiescent period or gap in volcanism upon arrival of the flat-slab associated with an extensive Farallon-North American lithosphere contact; and, 4) renewed volcanism usually in the form of ignimbrite flare-ups associated with the transition to steep slab and subsequent rollback. The marked age difference in post-angular unconformity ignimbrite deposits from north to south documented here is attributed to the early abutment and steepening of the flat-slab against a pronounced ancient cratonic lithospheric mantle keel east of the Davis Mountains in the north followed by rollback. A later related steepening perhaps facilitated by tearing of the slab in the southern Trans-Pecos area likely occurred with no direct collision of the flat-slab against a keel because of a less buoyant subducted lithosphere and less pronounced or absent cratonic lithospheric mantle keel to the south.application/pdfengThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).Trans-PecosLaramide orogenyZircon geochronologyIgnimbrite flare upsMagmatismTexasWest TexasBig Bend National ParkVolcanismSubductionFlat-slabGeology2014-07-24Thesisborn digital