GREAT BASIN PIERCING POINTS CONSTRAIN THE PROTEROZOIC LAURENTIA-SIBERIA CONNECTION

The Great Basin exhibits numerous geologic piercing points that constrain the Proterozoic Laurentia-Siberia continental reconstruction of Sears and Price (1978, 2003). Pre-rift links between the cratons include closely correlative Archean provinces, ~ 2.0-1.72 Ga Paleoproterozoic terranes and shear zones, ~ 1.5-1.0 Ga Mesoproterozoic mafic dike and sill swarms, and 1.5-1.2 Ga Mesoproterozoic intracratonic basins and congruent faults. The putatively conjugate Cordilleran and east Siberian Verkhoyansk margins exhibit correlative Cryogenian and Ediacaran-Early Cambrian rift phases with coeval fault zones, angular unconformities, bimodal syenite/trachyte assemblages, subsidence histories and detrital zircon suites. Post-rift links include endemic Early Cambrian fossil assemblages and early Paleozoic thermal subsidence profiles of the Cordilleran and Verkhoyansk passive continental margins.

The Great Basin occupied the outer proximal margin of Laurentia and included a graben system that captured thick Cryogenian diamictites, turbidites, and rift volcanics and Ediacaran and Early Cambrian rift volcanics and siliciclastics. Cryogenian and Cambro-Ordovician rift-related syenite intrusives peppered the Laurentian rift margin. On the Siberian side, Cryogenian and Ediacaran detrital zircons occur within Ediacaran and Early Cambrian arkosic sandstones and correlate with Laurentian intrusives and volcanics. The margins both record faulting and tilting at ~550 Ma, reflecting final rifting prior to their respective episodes of continental separation. The Siberian margin experienced Early Cambrian trachytic volcanism and intrusion, with pillowed trachybasalts, dikes, sills, breccia pipes, tuffs, and volcaniclastic sediments with pebbles of ultrapotassic trachyrhyolite porphyry (Prokovief et al., 2016). Early Cambrian (~520 Ma) trilobite genera Profallotaspis and Archaeaspis, are restricted to Siberian and Cordilleran sites proposed to represent adjacent conjugate basins. Both margins experienced rapid thermal subsidence beginning in Middle Cambrian time at the onset of continental drift. Paleomagnetism permits drift of the Siberian craton on a coast-parallel, dextral transform system from western Laurentia to its terminal collision with Europe along the Ural Mountains.