Geodynamic interpretation of Paleozoic tectonic trends oriented oblique to the Mesozoic Klamath-Sierran continental margin in California

Abstract

Devonian-Mississippian Antler and Permian-Triassic Sonoma orogenic trends are oriented northeast-southwest across Nevada and California at high angles to the Mesozoic-Cenozoic Cordilleran margin. The Roberts Mountains (Antler) and Golconda (Sonoma) allochthons of central Nevada were thrust over the miogeoclinal continental margin as accretionary prisms assembled and emplaced by episodic slab rollback toward the southeast during subduction downward to the northwest beneath an evolving offshore system of frontal and remnant magmatic arcs facing toward the continent. Diachronous Devonian and Permian arc assemblages forming superposed stratigraphic successions in the eastern Klamath Mountains and northern Sierra Nevada record alternating episodes of eruptive activity and dormancy along parallel but separate arc structures within the offshore island arc complex. Deformed lower Paleozoic rocks forming the substratum of the Klamath-Sierran arc assemblages display imbricated thrust panels shingled in a structural pattern indicative of southeast vergence within a regional accretionary prism that included the Roberts Mountains allochthon at its leading edge. Thrust emplacement of the Roberts Mountains allochthon over the miogeoclinal belt temporarily arrested subduction, to allow deposition of the Havallah sequence between the deformed continental margin and an offshore system of remnant island arcs. Renewed subduction and slab rollback emplaced the accretionary prism of the Golconda allochthon composed of the deformed Havallah sequence. Antler-Sonoma tectonic elements were truncated on the southwest by a sinistral late Paleozoic to earliest Mesozoic transform fault, which established the northwest-southeast trend of the California continental margin and displaced the miogeoclinal Caborca block southward into Mexico.