A BILLION-YEAR TALE OF TWO CRATONS: WYOMING-SUPERIOR NEOARCHEAN TO PALEOPROTEROZOIC SOJOURNS

Direct U-Pb dating of deformation coupled to paleomagnetic data from Archean and Proterozoic dyke swarms has established that southern Wyoming and southern Superior cratons sutured ca. 2.65 Ga along the Oregon Trail structural belt (OTSB) in central Wyoming and remained connected until the ca. 2.1 Ga breakup. Wyoming was likely part of a much larger, high-µ landmass, and this collision was a key step in formation of the supercraton Superia-Vaalbara. Superia-Vaalbara migrated to the equator ca. 2.45 Ga, was intruded by a series of LIPs, and records several Paleoproterozoic glaciations and oscillations in atmospheric redox state at the early stage of the Great Oxidation Event between ca. 2.43 and 2.32 Ga. In this reconstruction, the Huronian Supergroup, along the southern margin of the Superior craton, and the Snowy Pass Supergroup, along the southeastern margin of the Wyoming craton, were conjugate, coeval, and deposited in the same basin. Hearne and Kola-Karelia cratons were also conjugate to Wyoming and Superior at this time, based on coeval mafic magmatism and similar lithostratigraphic patterns in sedimentary successions. Breakup of the Superia-Vaalbara craton involved multiple rifts from 2.3 to 2.0 Ga and led to the first separations of the high-µ cratons: Pilbara, Kaapvaal, Wyoming, Hearne, and Kola-Karelia. Breakup of Wyoming and Superior occurred ~100 km south of the OTSB suture, leaving the Southern Accreted terrane (SAT) attached to the Wyoming craton and the Minnesota River Valley province, with affinities to Wyoming, to the Superior craton. By 1.90 Ga, Wyoming and Superior cratons were ~60° apart in longitude at mid-latitudes on the basis of the simplest drift paths and data from the Sourdough dike swarm. The Wyoming craton joined Laurentia by reconnecting with the Superior craton along the Wyoming craton's eastern margin ca. 1.72 Ga based on tectonic history of the Hartville Uplift and Black Hills. Collision with Laurentia to the north is manifested by the 1.74 Ga Big Sky orogeny in SW Montana, and evidence for ca. 1.74 Ga subduction along the Vulcan structure. This reconstruction splits the Trans-Hudson orogen into separate, older (northern) and younger (southern) orogens and the Yavapai province into similarly aged, but unrelated western and eastern provinces separated by the Central Plains orogen.