WYOMING ON THE RUN – TOWARD FINAL PALEOPROTEROZOIC ASSEMBLY OF LAURENTIA

Wyoming was the last craton to join Laurentia, ca. 1.72 Ga, after an independent run that followed the break-up of the Archean-Paleoproterozoic supercraton Superia. New paleomagnetic and geochronologic data from Archean and Proterozoic mafic dike swarms in the Wyoming craton establish that the Wyoming and Superior cratons were connected from ca. 2.65 to 2.1 Ga along their southern margins with the Huronian and Snowy Pass supergroups linked in a shared basin (e.g. Roscoe and Card 1993). The two cratons rifted ca. 2.1-2.0 Ga and were ~60° apart in longitude at mid-latitudes by 1.90 Ga on the basis of the simplest drift paths and data from the Sourdough dike swarm. Wyoming joined Laurentia by reconnecting to Superior along Wyoming's eastern margin ca. 1.72 Ga based on tectonic histories exposed in the Hartville Uplift and Black Hills.

This model requires a reinterpretation of the nature and timing of the Dakotan arm of the southern Trans-Hudson orogen (THO), and separates the tectonic histories of the western and eastern Proterozoic accreted terrains (formerly Yavapai) until at least 1.72 Ga. The arc terranes of the Colorado Province accreted to the Wyoming craton ca. 1.78 to 1.74 Ga. while it was independent. They are unrelated tectonically to similar-aged rocks in the Great Lakes region. We envision the 1.72 Ga suture as being a sigmoidal-shaped feature that links either the Vulcan structure in southern Alberta or the Big Sky Orogen in southern Montana to the Dakotan arm of the THO and the SE-trending arm of the Central Plains orogen. This new orogen is consistent with basement geophysical trends and supported by the recent BASE project in northeastern Wyoming that argued for a >150 km-wide Proterozoic orogenic belt immediately east of the Bighorn Mountains.