Tectonic setting and provenance of the Neoproterozoic Uinta Mountain and Big Cottonwood groups, northern Utah: constraints from geochemistry, Nd isotopes, and detrital modes
Kc. Condie et al., Tectonic setting and provenance of the Neoproterozoic Uinta Mountain and Big Cottonwood groups, northern Utah: constraints from geochemistry, Nd isotopes, and detrital modes, SEDIMENT GE, 141, 2001, pp. 443-464
The Neoproterozoic Uinta Mountain Group was deposited in an east-trending i
ntracratonic rift bounded on the north by an active fault system and openin
g into a shallow sea on the west where the Big Cottonwood Group was deposit
ed in an estuary. Although this rift may have been associated with the earl
y stages in the breakup of Rodinia, it was not an aulacogen. Geochemical, N
d isotope, and detrital mode studies indicate that Uinta Mountain Group sed
iments were derived from mixed Archean and Paleoproterozoic sources with th
e former dominating. Big Cottonwood Group sediments appear to have been der
ived predominantly from Paleoproterozoic sources. The Archean sediment sour
ce is the Wyoming craton, and source rocks comprised dominantly granites en
riched in Th, U, Y, Zr, Hf, and REE. The relative abundance of enriched gra
nite implied by sedimentary rocks of the Uinta Mountain Group indicates tha
t 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 up
lift in northwest Utah, possibly ancestral to the Paleozoic Toole-Uinta arc
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