Detrital zircon uranium-lead geochronology of the Schoonover Sequence (Golconda Allochthon, Nevada): Alternative paleogeography of the Havallah-Schoonover Basin with implications for Antler-SLaB-Sonoma orogenesis

Abstract

Detrital zircon UPb data (N = 3; n = 713) from the Lower Mississippian Schoonover Sequence support an alternative two-source provenance model for Carboniferous strata of the Golconda Allochthon that may have significant implications for late Paleozoic paleogeography and tectonism along the western margin of Laurentia. Existing models invoke derivation of quartzofeldspathic material within Schoonover-Havallah strata by erosion of the Roberts Mountain Allochthon coupled with simultaneous derivation of the volcanic component from the offshore Eastern Klamath-Northern Sierra arcs. Deposition of these two components occurred in a parautochthonous extensional basin that formed between the latest Devonian to Early Mississippian Antler and Permo-Triassic Sonoma compressional orogenies. In our alternative model, the quartzofeldspathic component of the ca. 350 Ma Schoonover Sequence was derived by erosion of Canadian passive margin strata and metamorphic equivalents exposed north of the submerged Peace River Arch; volcanic contributions were derived from the Yukon-Tanana Arc. This model implies that deposition of strata comprising the Roberts Mountain and Golconda allochthons occurred in transient, transtensional marine basins formed within a sinistral transcurrent plate boundary; local plate tectonic reorganization ended deposition in a given basin, followed by southward tectonic translation of basin strata.In this alternative model, the Antler and the Sonoma orogenies represent tectonic bookends of a single, ca. 100-Myr-long sinistral transcurrent orogeny. Continuous sinistral transcurrent deformation along the jagged western edge of Laurentia produced local stress variations that accommodated deposition in transtensional basins while deformation and translation of basin strata occurred along transpressional fault strands. A protuberance in the continent's rifted edge formed a barrier to continued southward transport along the inner edge of the transcurrent plate boundary, forcing far-traveled strata to sequentially pile up and form the Roberts Mountain and Golconda allochthons. Between allochthon emplacement, the focus of sinistral deformation stepped outboard within the broad Southwestern Laurentian Borderland (SLaB). The relative tectonic quiescence permitted local deposition of overlap and successor strata above the Roberts Mountain but below the subsequently overlying Golconda Allochthon; these strata record, however, multiple unconformities and deformation events indicating that deformation across the broad SLaB region continued between the Antler and Sonoma orogenies.