Tectonic setting and provenance of the Neoproterozoic Uinta Mountain and Big Cottonwood groups, northern Utah: constraints from geochemistry, Nd isotopes, and detrital modes Kent C. Condie a, * , Dennis Lee a , G. Lang Farmer b a Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA b Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA Accepted 19 January 2001 Abstract The Neoproterozoic Uinta Mountain Group was deposited in an east-trending intracratonic rift bounded on the north by an active fault system and opening into a shallow sea on the west where the Big Cottonwood Group was deposited in an estuary. Although this rift may have been associated with the early stages in the breakup of Rodinia, it was not an aulacogen. Geochemical, Nd isotope, and detrital mode studies indicate that Uinta Mountain Group sediments were derived from mixed Archean and Paleoproterozoic sources with the former dominating. Big Cottonwood Group sediments appear to have been derived predominantly from Paleoproterozoic sources. The Archean sediment source is the Wyoming craton, and source rocks comprised dominantly granites enriched in Th, U, Y, Zr, Hf, and REE. The relative abundance of enriched granite implied by sedimentary rocks of the Uinta Mountain Group indicates that the Wyoming craton is anomalous compared to other Archean cratons. CIA values and A±CN±K relationships in shales of the Uinta Mountain and Big Cottonwood groups indicate high degrees of weathering of sources, probably in subtropical to tropical climates supporting a near-equatorial location for southwestern Laurentia at about 800 Ma. Differences in the Nd isotopic composition between the Big Cottonwood Group and Neoproterozoic sedimentary rocks in western Utah and northeast Nevada suggest a northwest-striking uplift in northwest Utah, possibly ancestral to the Paleozoic Toole±Uinta arch. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Nd isotopes; Neoproterozoic; sediment provenance; rift basins 1. Introduction It is well known that part of the tectonic, climatic, and magmatic history of continents is retained in detrital sediments. Important in extracting this infor- mation are lithologic association petrotectonic assemblage), chemical and isotopic composition, and detrital mineralogy Dickinson et al., 1983; Taylor and McLennan, 1985; Roser and Korsch, 1988; McLennan et al., 1993). Furthermore, detrital sediments may be the only record we have of crust that has been removed by erosion, covered with younger deposits or ice, or buried deep in the crust. Sediment provenance can be tracked with trace elements, Nd and Pb isotopes, U/Pb detrital zircon ages, and detrital modes Taylor and McLennan, 1985; Sawyer, 1986; Condie and Wronkiewicz, 1990; Crichton and Condie, 1993; McDaniel et al., Sedimentary Geology 141±142 2001) 443±464 0037-0738/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0037-073801)00086-0 www.elsevier.nl/locate/sedgeo * Corresponding author. Tel.: 11-505-835-5531; fax: 11-505- 835-6436. E-mail address: kcondie@nmt.edu K.C. Condie).