Proterozoic evolution of the western margin of the Wyoming craton: implications for the tectonic and magmatic evolution of the northern Rocky Mountains

Abstract

Defining the extent and age of basement provinces west of the exposed western margin of the Archean Wyoming craton has been elusive because of thick sedimentary cover and voluminous Cretaceous-Tertiary magmatism. U-Pb zircon geochronological data from small exposures of pre-Belt supergroup basement along the western side of the Wyoming craton, in southwestern Montana, reveal crystallization ages ranging from -2.4 to -1.8 Ga. Rock-forming events in the area as young as -1.6 Ga are also indicated by isotopic (Nd, Pb, Sr) signatures and xenocrystic zircon populations in Cretaceous-Eocene granitoids. Most of this lithosphere is primitive, gives ages -1.7-1.86 Ga, and occurs in a zone that extends west to the Neoproterozoic rifted margin of Laurentia. These data suggest that the basement west of the exposed Archean Wyoming craton contains accreted juvenile Paleoproterozoic arc-like terranes, along with a possible mafic underplate of similar age. This area is largely under the Mesoproterozoic Belt basin and intruded by the Idaho batholith. We refer to this Paleoproterozoic crust herein as the Selway terrane. The Selway terrane has been more easily reactivated and much more fertile for magma production and mineralization than the thick lithosphere of the Wyoming craton, and is of prime importance for evaluating Neoproterozoic continental reconstructions.

Geometry of the Neoproterozoic and Paleozoic rift margin of western Laurentia: Implications for mineral deposit settings

“…The core of Laurentia is composed of Archean and Paleoproterozoic domains that were assembled in the Paleoproterozoic (Hoffman, 1988;Ross et al, 1991;Karlstrom et al, 2002;Sims et al, 2005;Foster et al, 2006). Across that Paleoproterozoic continental mass, isolated Mesoproterozoic basins were created in localized rifting events (Link et al, 1993;Price and Sears, 2000;Ross et al, 2001).…”

Dating Metasomatism: Monazite and Zircon Growth during Amphibolite Facies Albitization

“…These consist of Archean to Paleoproterozoic orthogneiss units with several suites of deformed intrusive mafic dikes and interleaved supracrustal metamorphic rocks [21][22][23][24]. The majority of these lithologies have Archean protoliths, and along the northwestern margin of the Wyoming province, they contain evidence for at least two high temperature thermotectonic events: the enigmatic 2500-2450 Ma Tobacco Roots-Tendoy orogeny [20,[25][26][27] and the 1800-1710 Ma Big Sky orogeny [20,22], interpreted as the results of the Wyoming province docking with the rest of the Archean core of Laurentia during the amalgamation of supercontinent Nuna [28,29]. To the southeast of the rocks overprinted by Paleoproterozoic thermotectonism, K-Ar and 40 Ar- 39 Ar thermochronology indicates that the Archean rocks have not been thermally overprinted since the Neoarchean (Figure 1A,B; [30][31][32]).…”

The effect of drainage reorganization on paleoaltimetry studies: An example from the Paleogene Laramide foreland

“…The more radiogenic Sr isotope composition of these samples reflects the radiogenic composition of Sr in adjacent, craton-cored Laramide structures (e.g., cores of the Wind River, Granite, Owl Creek, Laramie and Sierra Madre Uplifts were exposed in the Eocene Carroll et al, 2006), where whole rock 87 Sr/ 86 Sr ratios can be in excess of 1.0 (Divis, 1977;Peterman and Hildreth, 1978;Zielinski et al, 1981;Mueller et al, 1985;Frost et al, 1998;Patel et al, 1999). Although the Uinta Uplift bounding the Uinta Basin to the north is also basement-cored, the east-trending axis of the range is beyond the southwestern margin of the Wyoming craton, so that basement rocks at the core of the Uinta Uplift are a mixture of sediments deposited during the Neoproterozoic accretion of terranes (Ball and Farmer, 1998;Condie et al, 2001;Nelson et al, 2002;Foster et al, 2006 Sr ratios to also be high during the later stages of Lake Uinta's lifespan, when braided streams flowing south from the Uinta Uplift deposited fluvial units along the northern margin of the lake (Anderson and Picard, 1972;Davis et al, in press . Following the shift in Sr isotope composition at~53 Ma, the mean δ 18 O calcite value of coeval carbonates in the lower Main Body of the Uinta Basin's Green River Formation is similar: 24.9‰ (1σ = 3.5, n = 47).…”

“…Lack of covariance of C and O isotopes (Fig. 3) (Blum et al, 1998;Jacobsen and Blum, 2000;Gierlowski-Kordesch et al, 2008) and (2) the fact that few Precambrian basement rocks, which might have imparted a more radiogenic signature, were ever exposed south of the Uinta Basin except for the Front Range, which lay more than 300 km to the southeast (Foster et al, 2006). We interpret the increase in 87 Sr/ 86 Sr ratios in carbonate samples from Lake Uinta at~53 Ma as the result of a large-scale reorganization of the lake's drainage system with new and substantial inflows from Lake Gosiute and the catchments of the Greater Green River Basin that eventually extended into the Challis Volcanic Field at~49 Ma (KentCorson et al, 2006;Carroll et al, 2008 Sr ratios of samples from the Laney Member of the Green River Formation (~50 Ma) in the Greater Green River Basin (~285 km from our sampled section over the Uinta Uplift) give a mean of 0.71245 ± 0.00014 (n = 22, p b 0.05) (Rhodes et al, 2002).…”