THE AGE AND ORIGIN OF PRECAMBRIAN ORTHOGNEISS OF THE GROUSE CREEK BLOCK, NORTHERN UTAH AND SOUTHERN IDAHO

New geochronologic and isotopic analyses from the Grouse Creek block (GCB) provide insight into the assembly of western Laurentia during the late Archean to Paleoproterozoic and establish the influence of the GCB in the evolution of Yellowstone-Snake River Plain hotspot magmatism in the central Snake River Plain. The GCB is primarily exposed in the Albion-Raft River-Grouse Creek metamorphic core complex of northern Utah and southern Idaho and includes a complex assemblage of orthogneiss, schist, amphibolite, and metasediments intruded by Oligocene plutons and overlain by Cenozoic sedimentary units. Many investigations of the GCB have focused on the structural evolution of the Albion-Raft River-Grouse Creek metamorphic core complex (ARG), but few have concentrated on the precise age and origin of exhumed igneous rocks and their relation to neighboring Archean terranes and the Yellowstone-Snake River Plain (YSRP) volcanic province. Orthogneiss has been sampled from three locations within the ARG for U-Pb geochronologic and Hf isotopic analyses of igneous and metamorphic zircons, along with whole rock geochemistry. These data will be compared to existing regional data sets to add to our understanding of the age and origin of the GCB, its influence on YSRP hotspot magmatism, and the construction of western Laurentia.