AGE AND EVOLUTION OF THE FARMINGTON CANYON COMPLEX, NORTHERN UTAH: INSIGHTS FROM U-PB ZIRCON GEOCHRONOLOGY

Basement rocks of the Farmington Canyon Complex (FCC) exposed in northern Utah provide a window into the crustal evolution between the Archean Wyoming Province and Grouse Creek block. The FCC is comprised of granitic orthogneisses, a range of paragneisses containing metaquartzite and sillimanite-bearing schist, and amphibolite that underwent polyphase deformation and high-grade metamorphism, along with late-stage leucogranites and pegmatites. Previous studies have identified inheritance of Archean components and late Paleoproterozoic metamorphism in sampled lithologies. Provenance and depositional ages of paragneiss protoliths, and geochemical signatures and ages of some igneous units, however, remain poorly constrained, partly due to a complex history. For this study, systematic sampling of multiple lithologies (paragneiss, metaquartzite, orthogneiss, and late leucogranite) spanning northern, southern, and western exposures of the FCC in the Ogden, Bountiful Peak, and Antelope Island areas was completed. Zircon grains were separated using standard techniques, imaged using cathode luminescence to identify cores and growth zones, and analyzed by LA-ICPMS using a small spot size (20 µm). This approach was designed to constrain the provenance and ages of paragneiss protoliths, ages of igneous and xenocrystic zircon in orthogneiss units, metamorphic ages of zircon rims, and ages of leucogranites that bracket end of major deformation. Preliminary data show that different paragneiss samples have varying proportions of (i) 2.7-2.6 Ga plus some older cores likely sourced in part from the Wyoming Province; (ii) 2.6-2.5 Ga cores possibly sourced from the Grouse Creek block; (iii) a mode of 2.45 Ga cores likely sourced from local granitic intrusions; and (iv) ~2.3-2.0 Ga cores, similar to ages of strata along the southern rifted margin of the Wyoming Province. Zircon rims have low Th/U and dates of 1.7-1.6 Ga across the FCC that record regional peak metamorphism. Some orthogneiss samples contain a mode of 2.45 Ga grains related to early intrusions. Additional orthogneiss and leucogranite samples have been collected and will be run for U-Pb and Hf to evaluate the potential for multiple igneous intrusions, crustal recycling, and relationships to paragneiss units.