PROTEROZOIC ACCRETION OF WESTERN LAURENTIA WITH IMPLICATIONS FOR NUNA AND RODINIA RECONSTRUCTIONS

Most reconstructions for Rodinia or pre-Rodinia supercontinents assume that the southwestern margin of Laurentia consists of separate Mojave, Wyoming, and Hearn-Medicine Hat crust, with or without the extension of the Great Falls tectonic zone. Significantly different interpretations for the nature of this crust have clouded correlations to potential conjugates. The original AUSWUS correlation extended southern Laurentian belts into Australia, even though the age and orientations of adjacent belts did not readily fit. SWEAT extended Wyoming Archean along the entire western margin, complicating matches with late Archean cratons in Antarctica-Australia. Recent evidence for Laurentian detritus in East Antarctica builds on previous correlations based on Nd-isotopic mapping. The Mojave province is frequently compared to the eastern margin of the Gawler craton (Broken Hill-Olary) or Mount Isa. The ages and isotopic compositions of rocks within the Selway, Farmington, Priest River, and Grouse Creek domains of western Laurentia suggest affinities with Mojave; with differences confined to relative proportions of latest Archean (2.6-2.5 Ga) and earliest Paleoproterozoic (ca. 2.45 Ga) crust along with late Paleoproterozoic-early Mesoproterozoic juvenile rocks and orogenic reworking. Convergence of a composite Mojave to Priest River terrane (and trailing continent?) with Laurentia occurred between about 1.73 and 1.67 Ma due to subduction directed away from Laurentia, eventually forming a suture extending along the western margin of Wyoming and Hearne cratons. Key in this interpretation is that the Cheyenne belt does not extend west to the rifted margin, but curves south to become the boundary between Mojave and Yavapai where it separates evolved and more juvenile lithosphere. This reconstruction provides for better correlations between Australia-Mawson, North China, and Laurentia prior to formation of Rodinia, and is consistent with the isotopic composition and detrital zircons of the Belt basin strata. The model gives a framework for correlating world-class base metal deposits in western North America and Australia within a continuous, metal sulfide-rich, Paleoproterozoic, suprasubduction zone, lithospheric section that was tapped during later metallogenic magmatic and hydrothermal events.