The Basin and Range Province as a Composite Extensional Domain

Abstract

The Basin and Range province is a composite Cenozoic taphrogen with a present configuration and internal geometry derived from superimposed multiple phases of extensional deformation driven by varied geodynamic impulses. Different components of the composite taphrogen derive from: (a) post-orogenic Late Paleocene to Middle Miocene slab rollback beneath overthickened crust of the Sevier-Laramide orogen, to induce migratory arc magmatism, tectonic denudation of Cordilleran metamorphic core complexes within associated domains of crustal extension, and belts of backarc rifting including pre-Middle Miocene phases of the Rio Grande rift; (b) Eocene transrotational tectonism that pivoted and displaced crustal elements of the Paleogene forearc in the Pacific Northwest; (c) late Early Miocene and younger crustal extension in the northwestern Basin and Range province (Numic subtraphrogen including segments in the Great Basin, Southeast Oregon Plateau, and Idaho-Montana border regions) as structural accompaniment to northward migration of the Mendocino triple junction; and (d) late Middle Miocene and younger crustal extension in the southeastern Basin and Range province (Piman subtaphrogen including the Gulf of California extensional province, interior Meseta Central province, and post-mid-Miocene Rio Grande rift) succeeding the rapid southward migration of the Rivera triple junction. A transtaphrogen bridge spanning the Mojave block, Eastern Transverse Ranges, and a broad region in southeastern California and southwestern Arizona experienced only limited post-mid-Miocene extensional deformation during evolution of the active Numic and Piman subtaphrogens lying to the northwest and southeast. The compound evolutionary history of the Basin and Range province renders moot any unitary theories for its geodynamic behavior.