2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 3
Presentation Time: 8:00 AM-12:00 PM


MUELLER, Paul A., Geological Sciences, Univ of Florida, Gainesville, FL 32611, FOSTER, David, Department of Geology, University of Florida, Gainesville, FL 32611, MOGK, David, Earth Sciences, Montana State Univ, Bozeman, MT 59717, WOODEN, Joseph, USGS-SUMAC, Stanford Univ, Stanford, CA 94305-2220, VOGL, James, Department of Geology, Univ of Florida, Gainesville, FL 32611 and KAMENOV, George D., Department of Geological Sciences, University of Florida, 241 Williamson Hall, PO Box 112120, Gainesville, FL 32611, mueller@geology.ufl.edu

The Uinta Mountain Group (UMG) consists primarily of clastic sedimentary rocks of fluvial origin deposited in a Neoproterozoic, fault-bounded basin between the Archean crust of the Wyoming province and the Paleoproterozoic crust of the Yavapai-Mazatzal terranes. The UMG rests unconformably on dominantly Paleoproterozoic metamorphic rocks of the Red Creek quartzite and the Owiyukuts gneisses that appear to be older than adjacent Yavapai-Mazatzal crust (~1.6-1.8 Ga). The ages of detrital zircons from the UMG, however, do not correspond to a simple mixture from these three adjacent Precambrian terranes. Instead, U-Pb ages of detrital zircons from two arkosic sandstones (UMG-1, 2) are dominantly (>90%) 2.5-2.8 Ga and correspond closely to ages of rocks in the southern Wyoming province. Detrital zircons from a quartz arenite and a feldspathic sandstone (UMG-3, 4), however, yield U-Pb ages that are dominantly (>70%) Grenvillian (~0.95-1.35 Ga) and Archean (~20%) with few intermediate ages. In order to further constrain the origin of the Grenville-age zircons, we conducted 1) total laser fusion and limited step-heating experiments on individual white micas from a silty lens within UMG-2 (=2B) and UMG-4 and 2) Lu-Hf isotopic measurements of zircon from UMG-3, 4. Mica ages from UMG-2B range from ~0.6 to 1.6 Ga and are compatible with a late Neoproterozoic depositional age for the UMG and a possible contribution of detritus from Yavapai-Mazatzal rocks. Analyses of micas from UMG-4 (feldspathic sandstone), however, yielded a much different range of ages (~0.3 to 2.45 Ga). Void-filling secondary seritization in UMG-4 suggests the Paleozoic Ar ages may be artifacts of alteration, but does not obviate the co-occurrence of feldspar and Archean grains in these rocks. Epsilon Hf of zircons from UMG-3 and 4 averages about –22, which suggests derivation from older crust reworked during the Grenville orogeny. Overall, these results point to a major change in provenance and sedimentary processes in Laurentia and/or its Neoproterozoic conjugate during deposition of the UMG that included rapid removal of new and recycled Archean zircons from the sedimentary cycle and a substantial flood of Grenville-age detritus to the exclusion of detritus from adjacent older crust.