ISOTOPIC ANALYSES OF THE GROUSE CREEK BLOCK: A LINK TO THE WYOMING CRATON?

The extent and proportion of Archean and Proterozoic rocks along the western margin of the Wyoming craton is poorly constrained. Determining the extent of the Wyoming craton is central to testing models of Proterozoic conjugates to the Laurentian margin. Proposed models of Proterozoic paleogeographical reconstructions rely heavily on piercing points to link once adjoined segments of crust. One must first know the extent of the Archean Laurentian crust in order to establish viable piercing points. Located to the west of the Wyoming craton, the Grouse Creek block has limited exposures of Archean rocks within the Grouse Creek and Albion ranges. The Grouse Creek block is separated from outcrops of the Archean Wyoming craton by Paleoproterozoic rocks within the Farmington Zone. It is unclear, however, if the Grouse Creek block is distinct from the Wyoming craton at depth. The Grouse Creek block could be an accreted allochthonous Archean block, a rifted fragment of the Wyoming craton that re-accreted, or part of the Wyoming craton separated by a Paleoproterozoic intracratonic rift and mobile belt. Determining the relationship between the Grouse Creek block and the Wyoming craton is crucial in elucidating the character of the Farmington Canyon Complex of Northeastern Utah. The Wyoming craton is characterized by an enriched ²⁰⁷Pb/²⁰⁴Pb isotopic signature that distinguishes it from all other Archean provinces and is thought to represent early crustal extraction. The Pb ratios unite the Wyoming Province as a single Archean block or group of blocks that formed proximal to each other under similar processes. In addition to the Pb-isotopic data, the Wyoming Province is characterized by Sm-Nd model ages and rock ages to 4.0 Ga. Lead and neodymium isotopic signatures of rocks from the Grouse Creek block were compared to the isotopic signatures of the Wyoming craton to determine if the Grouse Creek block is correlative to Wyoming. Preliminary data suggest the Pb isotopic signature of the Grouse Creek block is unique and that the Grouse Creek block represents an allochthonous terrane accreted to the western margin of the Wyoming craton during the Paleoproterozoic.