Paleoproterozoic evolution of the Farmington zone: Implications for terrane accretion in southwestern Laurentia

Abstract

Precambrian rocks in the Farmington zone in northeastern Utah provide important constraints on the accretionary history of southwestern Laurentia because they lie at the orogenic intersection of the Wyoming, Yavapai-Colorado, and Mojave provinces. Approximately 200 U-Pb analyses of zircons from Paleoproterozoic rocks in the Wasatch Mountains (Farmington Canyon and Little Willow complexes) and Uinta Mountains (Owiyukuts and Red Creek complexes) indicate: (1) U-Pb ages of 2.446 ± 0.011 Ga for igneous zircons from a meta-igneous rock and 2.42 Ga for the youngest detrital zircon from a metasedimentary rock constrain the age of the Farmington Canyon complex and represent a heretofore unreported Paleoproterozoic event in southwestern North America; (2) Most lithologies in all areas are metasupracrustal and U-Pb ages of most detrital zircons and whole-rock Sm-Nd data clearly indicate a primarily Archean provenance for the metasedimentary rocks; and (3) Metamorphism, including partial melting, occurred at 1.674 ± 0.012 Ga (2σ) based on U-Pb ages of 36 of 38 zircons (overgrowths and whole grains with Th/U <0.1) from metamorphic rocks, including leucosomes, from both the Wasatch and Uinta Mountains. These observations combined with previous work suggest a geologic history that begins with development of a Paleoproterozoic passive or rifted margin along the southwestern edge of the Wyoming craton and terminates with Paleoproterozoic accretion of Mojavia (±Yavapai-Colorado) to the Wyoming Province. Crystallization and model ages of the Farmington sequence suggest a possible genetic link between Mojavia, the Farmington zone, and the Wyoming Province, which would provide new constraints on proposed Neoproterozoic conjugates and the role of the Cheyenne belt in the accretionary tectonics of southwestern Laurentia.

Crustal growth and tectonic evolution of the Mojave crustal province: Insights from hafnium isotope systematics in zircons

“…2.6 Ga have been reported. Thus, although there are important geochemical similarities between Mojave and Wyoming province lithosphere (e.g., U-Th-Pb systematics), the paucity of 2.7 Ga and older zircons in the Mojave province suggests that physical mixing of Wyoming province crust into the nascent Mojave province was very limited (e.g., Mueller et al, 2011). Alternatively, the 2.6-2.4 and 2.0-1.8 Ga components may have been derived from an unexposed part of the Mojave province (Whitmeyer and Karlstrom, 2007), or an older crustal block that lay to the west (Barth et al, 2009).…”

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]).…”

Crustal Shear Wave Velocity Structure of Central Idaho and Eastern Oregon From Ambient Seismic Noise: Results From the IDOR Project

“…The discernible Phanerozoic history of the study area began with formation of a rifted passive margin along western Laurentia during Neoproterozoic-Cambrian time (Bond et al, 1984;Colpron et al, 2002;Lund, 2008;Stewart, 1972); this passive margin endured until the Devonian (Lund, 2008;Pyle & Barnes, 2003). The Precambrian basement east of the WISZ consists of an assemblage of Proterozoic and Archean terranes (Foster et al, 2006;Gaschnig et al, 2013;Hoffman, 1988;Karlstron et al, 2002;Mueller et al, 2011;Ross, 1991;Sims et al, 2005), including the Selway and Grouse Creek basement blocks and the western part of the Wyoming craton (Figure 1, e.g., Foster et al, 2006;Mueller et al, 2011;Sims et al, 2005). (Gaschnig et al, 2011) divides Blue Mountains Province to the west from Precambrian North America to the east (modified from Davenport et al, 2017, Figure 1 Paleoproterozoic basement of the Selway terrane, comprising predominantly 1.6-to 2.4-Ga-age metamorphic and igneous rocks (Foster et al, 2006) with some remnant Precambrian sedimentary cover of the Belt (Lemhi; 1470-1380 Ma) and Windermere (<850-600 Ma) Supergoups, underlies the northeastern part of the study area ( Figure 1).…”

“…The discernible Phanerozoic history of the study area began with formation of a rifted passive margin along western Laurentia during Neoproterozoic‐Cambrian time (Bond et al, ; Colpron et al, ; Lund, ; Stewart, ); this passive margin endured until the Devonian (Lund, ; Pyle & Barnes, ). The Precambrian basement east of the WISZ consists of an assemblage of Proterozoic and Archean terranes (Foster et al, ; Gaschnig et al, ; Hoffman, ; Karlstron et al, ; Mueller et al, ; Ross, ; Sims et al, ), including the Selway and Grouse Creek basement blocks and the western part of the Wyoming craton (Figure 1, e.g., Foster et al, ; Mueller et al, ; Sims et al, ).…”

“…The Selway-Grouse Creek boundary is entirely cryptic but implied by the occurrence of 2.55-to 2.65-Ga-age zircons within only the southern Late Cretaceous Atlanta lobe of the IB (Gaschnig et al, 2013). South of the IDOR Passive deployment footprint, in Utah, the Farmington zone separates the Wyoming craton and the Archean Grouse Creek block (Figure 1;Foster et al, 2006;Mueller et al, 2011). The extension of this zone north into Idaho and SW Montana is consistent with exposures of similar aged rocks in SW Montana (∼2.4 Ga; Foster et al, 2006), and with a clear Moho offset within the IDOR footprint that is coincident with the presumed surface trace of the Farmington zone (Stanciu et al, 2016).…”