TECTONIC EVOLUTION OF SOUTH-CENTRAL LAURENTIA - THE WEST TEXAS NEXUS

Colliding cratons and continents, opening and vanishing oceans, accreting and retreating fragments have shaped this margin for >1.3 Ga. Diagnostic elements of the progression are preserved in West Texas, where W. R. Muehlberger left brobdingnagian bootprints on structures of all vintages.

Paleoproterozoic – Mesoproterozoic. Metaigneous/metasedimentary strata of the Carrizo Mts. and Van Horn area attest to Paleo- to Mesoproterozoic tectonism: intraplate rifting (1380-1327 Ma); continental margin basin development; Grenvillian (~1000 Ma) collision/transpression. In the Franklin Mts., a 1250-Ma metamorphic suite was intruded at 1120 Ma by granites coeval in part with the Pecos mafic complex (1163-1073 Ma).

Neoproterozoic –Early Paleozoic. New data on Rodinia breakup, Iapetus opening, and Laurentia → Gondwana terrane transfer come from Marathon Basin. Boulders of unmetamorphosed volcanics in Ordovician conglomerates yield Paleoproterozoic- Cryogenian ages; a 706-Ma suite reflects early Rodinia rifting. With continued oblique dextral separation of Laurentia and Gondwana, the Ouachita-Cuyania basin formed; Cuyania split from Laurentia and was later accreted to Gondwana.

Late Paleozoic. Pangaea assembly produced both thin-skinned and basement-cored structures – 1) Marathon fold-thrust belt, 2) Ancestral Rocky Mountain uplifts (Diablo and Central Basin Platforms) and basins (Delaware, Midland, Val Verde).

Mesozoic. Evaporites deposited during J-K opening of Chihuahua Trough form cores of Laramide folds in the Chihuahua Tectonic Belt; Sa. del Carmen exemplifies the basement-cored uplifts. Left-transpressive structures are now documented within Mariscal Mt. Also in Late Cretaceous time (~77 Ma) basaltic phreatomagmatic magmatism of the Balcones intraplate igneous province extended westward into Big Bend.

Cenozoic. Voluminous Paleogene volcanics issued from multiple vents (e.g., Davis Mts.). Neogene Rio Grande rifting with bimodal magmatism began at ~30 Ma and created northerly grabens (e.g., Salt Basin). The Border Corridor transform zone – a system of northwesterly transtensional basins and westerly transfer zones (e.g., Tascotal Mesa) – links rift segments from Mesilla graben, SE to the Sunken Block. Strong earthquakes – Alpine, 1995 (M 5.7) – continue in the rift-transform complex.