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

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.