THE CONTINUOUS ROCK SPRINGS – DOUGLAS CREEK UPLIFT AND A FOLDING MECHANISM FOR LARGE-SCALE CONTROL OF ROCKY MOUNTAIN UPLIFTS

The Rock Springs (WY) – Douglas Creek (CO) uplifts are Laramide-age, NS-oriented, intrabasinal uplifts. Seismic data and sedimentary relations indicate that these uplifts follow no pre-existing structures. The sediments preserved in the basins, combined with a regional gravity survey, allow us to characterize the timing and structural evolution of these structures. A new gravity survey was completed and added to the USGS gravity data in the region, indicates that these uplifts are structurally continuous across the EW-oriented Uinta uplift, as delineated by.a gravity high continuous along the trend of the uplift. This structural high is supported by the occurrence of the only outcrops of the Owiyukuts Complex, the basement of the Uinta Mountain group, in the Uinta mountains along the trend of the Rock Springs – Douglas Creek uplift. The significance of a continuous Rock Springs – Douglas Creek uplift is that these uplifts occur in different continental crusts, the Wyoming province to the north and the Proterozoic terranes to the south. While pre-existing, crustal structures control the local geometry of the Laramide uplifts, they appear not to control the larger structural pattern. Uplift of the Rock Springs and Douglas Creek uplifts occurred in two pulses: Late Cretaceous and Eocene.The sedimentation patterns in both uplifts indicate that these uplifts originated as broad, arch-like structures in the Cretaceous (similar to ideas of Burg, 1961). The uplifts were reactivated in the Eocene by progressive tightening, and the uplifts were offset (24 km) by left-lateral movement within the Uinta mountains. The Cretaceous deformation appears to be well characterized by folding, presumably controlled by the lithospheric mantle since the crustal thicknesses are significantly different on either side of the Uinta uplift. One test to the folding model is the detailed Moho geometry below the uplifts, provided that Eocene reactivation has not significantly altered the Cretaceous geometry.