Petro-tectonic analysis of the Farmington Canyon Complex, Utah: Implications for... - Adolph Yonkee

Petro-tectonic analysis of the Farmington Canyon Complex, Utah: Implications for Paleoproterozoic rifting of Superia and assembly of Laurentia
Adolph Yonkee
-Department of. Earth & Environmental Sciences, Weber State University
The ages and isotopic signatures of basement rocks of the Farmington Canyon Complex (FCC), exposed in northern Utah, provide insight into the breakup of the supercontinent Superia and subsequent construction of Laurentia during the Paleoproterozoic. Rock types 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, plus late-stage leucogranite. 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 most igneous plutons and dikes remained poorly understood. For this study, systematic sampling, petrographic, and geochronologic analysis of varied rock types were completed. Zircon grains were imaged by SEM-CL to identify growth zones, and analyzed using LA-ICPMS to determine U-Pb dates and Hf isotopic signatures. Orthogneiss from multiple plutonic bodies with A-type granitic geochemical signatures have 2.45 Ga igneous zircon dates and epsilon Hf values of +3 to -3, indicating interaction with older crustal material or an enriched mantle source. Amphibolite from various mafic bodies with rift-related geochemical signatures have 2.45 and 2.12 Ga zircon dates. Paragneiss, metaquartzite, and schist samples contain abundant 2.9-2.55 Ga (plus older) detrital zircon cores with varying Hf isotopic signatures sourced from Archean crustal blocks, a mode of 2.45 Ga cores sourced from local plutons, and 2.3-1.9 Ga cores with juvenile Hf signatures likely related to syn-depositional igneous activity. Metamorphic zircon rims with high U/Th ratios have 1.8 to 1.6 Ga U-Pb dates that record protracted high-grade metamorphism during polyphase deformation. Small leucogranite plutons intruded near the end of deformation have dates of 1.68 to 1.62 Ga. Rocks of the FCC, including 2.45 Ga bimodal granitic plutons and mafic bodies, 2.12 Ga mafic dikes, and Paleoproterozoic meta-sedimentary rocks that incorporated materials eroded from Archean blocks, share similarities with parts of the southern Wyoming Province, southern Superior Province, and Kola-Karelia blocks, likely related to plume activity and rifting of Superia. Protracted 1.8-1.6 Ga metamorphism and intense deformation in the FCC, and in the Mojave and Yavapai Provinces to the south, record subsequent assemblage of crustal blocks with prior rifted margins, and arc-related rocks to form part of ancestral Laurentia.