AGE, PROVENANCE, AND HF ISOTOPIC SIGNATURES OF THE FARMINGTON CANYON COMPLEX, NORTHERN UTAH: IMPLICATIONS FOR PALEOPROTEROZOIC CRUSTAL EVOLUTION OF WESTERN LAURENTIA

The age and isotopic signatures of the Farmington Canyon Complex (FCC), exposed in northern Utah, provide insight into the construction of Laurentia during the Paleoproterozoic. Lithologies in the FCC include large bodies of granitic orthogneiss, paragneiss with layers of metaquartzite and schist, and amphibolite that all underwent polyphase deformation and high-grade metamorphism, and late-stage leucogranite and pegmatite. Although previous studies had identified inheritance of Archean components and late Paleoproterozoic metamorphism, provenance and depositional ages of lithologically varied meta-sedimentary rocks and isotopic signatures and ages of multiple igneous bodies remained poorly understood. For this study, systematic sampling of orthogneiss, amphibolite, paragneiss, metaquartzite, schist, and late leucogranite spanning FCC exposures in the Wasatch Range and on Antelope Island was completed. Zircon grains were separated, imaged by SEM-CL to determine growth zones, and analyzed using LA-ICP-MS to determine U-Pb radiometric dates and Hf isotopic signatures tied to crustal evolution. Orthogneiss samples from multiple plutonic bodies contain 2.45 Ga igneous zircon grains with epsilon Hf values ranging from +3 to -3, requiring an enriched mantle source or incorporation of older crustal material. Paragneiss and metaquarzite samples have varying proportions of older cores with varying Hf isotopic signatures sourced from Archean crustal blocks, a mode of 2.45 Ga cores likely sourced from local granitic plutons, and 2.3-2.0 Ga cores with juvenile Hf signatures interpreted to record syn-depositional igneous activity. Metamorphic zircon rims have low Th/U ratios and a range of 1.8 to 1.6 Ga dates that record protracted high-grade metamorphism and deformation. An abundance of 2.45 Ga granitic magmatism and associated mafic bodies, later Paleoproterozoic deposition of strata that incorporated materials eroded from Archean blocks, and 1.8-1.6 Ga metamorphism in the FCC share similarities with the southern part of the Wyoming Province and may record construction and rifting of Superia, followed by assemblage of crustal blocks to form ancestral Laurentia.