AGE, PROTOLITHS, AND PETROTECTONIC HISTORY OF THE FARMINGTON CANYON COMPLEX: PALEOPROTEROZOICEVOLUTION OF WESTERN NORTH AMERICA

Basement rocks of the Farmington Canyon Complex (FCC) exposed in northern Utah provide a window into crustal evolution between the Archean Wyoming Province and Grouse Creek block. The FCC comprises large granitic orthogneiss plutons and a supracrustal sequence of paragneiss, metaquartzite, schist, and amphibolite that were deformed, metamorphosed, and intruded by late-stage leucogranites during the Paleoproterozoic. Although prior studies provided broad geochronologic constraints, maximum depositional ages (MDAs) and provenance of the metasedimentary rocks and their relationships to orthogneiss plutons remained largely unknown. For this project, regional sampling of paragneiss, metaquartzite, orthogneiss, and leucogranites was completed. Zircon grains were separated and analyzed to determine U-Pb radiometric dates and Lu-Hf isotopic ratios related to crustal evolution. Thin sections were also analyzed to determine mineral assemblages and compositions. Samples from orthogneiss plutons and a layered mafic body contain 2.45 Ga igneous grains with εHf(t) values of +5 to -5, interpreted to record partial melting of variably depleted mantle and interaction with Neoarchean crust, possibly during plume activity and initial breakup of Superia. Paragneiss and metaquartzite samples contain varying age distributions of detrital zircon cores recording multiple source areas. Samples with abundant 2.7-2.6 Ga plus older Archean cores were likely sourced from the Wyoming Province, samples with abundant 2.6-2.5 Ga cores record sources from the Grouse Creek block, 2.45 Ga cores record input from granitic plutons that likely formed the basement to the supracrustal sequence, and ~2.3-2.0 Ga cores provide MDAs and reflect sources along the rifted margin of the Wyoming Province. Mineral abundances and geochemistry of paragneiss samples are consistent with a range of lithic to felsic-wacke protoliths. Metamorphic zircon rims with low Th/U in paragneiss, and igneous zircon grains in late leucogranite bodies, have dates of 1.75-1.6 Ga, recording protracted metamorphism during amalgamation of cratonic blocks and arc terranes to form SW Laurentia. Leucogranties have evolved zircon εHf(t) values of -10 to -15, and were likely derived from partial melting of paragneiss.