CRUSTAL STRUCTURE AND SUBSIDENCE MECHANISM OF THE WILLISTON BASIN FROM RECEIVER FUNCTIONS

The Williston Basin is bounded by Precambrian cratons with the Superior Craton to the east, Wyoming Craton to the west, and Hearn-Rae Craton to the north. In spite of numerous geological, geophysical, and geodynamic investigations conducted in the basin, the structure, origin, and subsidence are still not clear. In this study, we use P-to-S receiver functions recorded by about 200 USArray and other stations in the basin and adjacent areas to image crustal structure of the basin. After the removal of strong reverberations associated with a layer of Phanerozoic sediment with a thickness up to 4.5 km, a Moho doublet is clearly imaged beneath the basin. The top interface has a depth of about 40 km at the depocenter. This interface joins with the Moho beneath the western margin of the Superior Craton, where the crust is about 30 km thick and is most likely underlain by a low density upper mantle. The deeper interface, which is considered to be the petrological Moho, has a depth of 55 km beneath the Wyoming Craton, and deepens to about 75 km beneath the depocenter of the basin. The layer between the two interfaces represents a high density, probably eclogitized or garnet-rich lower crustal layer. Results from this first receiver function image of sub-sedimentary crustal layering of the basin are in agreement with the hypothesis that continuous retrograde metamorphism reactions from the Cambrian to Jurassic resulted in the nearly linear rather than exponential rate of subsidence of the basin as a consequence of crustal thickening associated with the Trans-Hudson Orogeny.