UNRAVELING THE PALEOPROTEROZOIC PETRO-TECTONIC EVOLUTION OF THE FARMINGTON CANYON COMPLEX, NORTHERN UTAH, IMPLICATIONS FOR THE BREAKUP OF SUPERIA AND CONSTRUCTION OF WESTERN LAURENTIA

The Farmington Canyon Complex (FCC) in northern Utah records a protracted Paleoproterozoic history of igneous intrusions, deposition of supracrustal units, and polyphase deformation. The FCC comprises granitic orthogneiss, paragneiss containing lenses of metaquartzite and sillimanite-bearing schist, and amphibolite that underwent intense deformation and high-grade metamorphism and were then intruded by late-stage leucogranites and pegmatites. Although previous studies had identified inheritance of Archean components and Paleoproterozoic metamorphism, provenance and depositional ages of paragneiss, and ages of most igneous units remained poorly constrained. Herein we report results from systematic sampling and U-Pb zircon geochronologic analysis of lithologies spanning exposures of the FCC in northern Utah. Zircon grains were separated using standard techniques, imaged using CL to identify cores and growth zones, and analyzed by laser ablation, an approach designed to determine provenance of paragneiss using core age distributions, ages of igneous zircon in orthogneiss and leucogranites, and metamorphic ages of rims. Granitic orthogneiss samples taken from large bodies interpreted as plutons, and from an associated layered mafic body, have consistent 2.45 Ga dates. The orthogneiss has A-type granite geochemistry and slightly evolved Hf isotopic signatures, and along with associated mafic bodies is interpreted to record plume magmatism. The granites and mafic bodies have similar ages as bimodal igneous rocks along parts of the edges of the Wyoming Superior, Rae-Hearne and Karelia provinces, consistent with a position in the middle of the proposed Superia continent at the onset of rifting. Paragneiss samples have varying proportions of 2.7-2.5 Ga plus older cores likely sourced from the Wyoming Province, a mode of 2.45 Ga cores likely sourced from the early granitic intrusions and 2.3-2.0 Ga cores that provide maximum depositional ages, similar to DZ age spectra of strata along the southern rifted margin of the Wyoming Province. Zircon rims have low Th/U and dates of 1.8-1.6 Ga that record timing of protracted, high-grade metamorphism, consistent with protracted deformation during accretion/ collision of the FCC and Wyoming, Mojave, and Yavapai provinces during growth of western Laurentia.