Archean Origins to the Lithospheric Architecture of the Wyoming Craton: A Test for Earthscope

Archean Wyoming craton comprises two main crustal domains, a central core (the Bighorn subprovince) with rocks as old as 3.5 Ga, dominated by voluminous magmatism ca. 3.3 Ga and 2.95-2.85 Ga, and a southern domain (Sweetwater subprovince and Southern accreted terrane) dominated by lateral accretion of juvenile terranes and microcontinents ca. 2.67 to 2.62 Ga. The Deep-Probe geophysical transect imaged distinctive lithospheric architectures in these two regions. The central core has a thick crust (50 to 60 km) and a pronounced fast lower crustal layer that is 20 to 25 km thick. Crust beneath the southern domain is thinner (45 km) and lacks the pronounced fast lower crustal layer that is present to the north. The transition occurs beneath a major geologic deformation zone, the Oregon Trail Structural belt, which was active 2.65 to 2.62 Ga. These correlations suggest that the lithospheric architecture is largely inherited and preserved from Archean lithospheric growth processes. One test of this hypothesis will come from the results of Earthscope's Transportable Array (TA) as it will determine the lateral extent of the distinctive lithospheric contrasts imaged by the 2-D Deep-Probe experiment, and whether there are regionally extensive correlations between crustal history and lithospheric architecture. The central core contains few to no xenoliths for directly dating the age of the lower crust and mantle.

Results from the current deployment of the TA, coupled to data from several high-density arrays near Yellowstone, have established that thick crust and the pronounced fast lower crust are present west of the Deep-Probe transect. Data from summer 2008 TA deployment will test the correlations for southern and eastern Wyoming craton. If the correlations hold, the TA experiment will strengthen a model that the lower crust and subcontinental mantle of the Wyoming craton are Archean in age.