Geochemistry and tectonic setting of Early Proterozoic supracrustal rocks in the southwestern United States

A revision of previous models of Proterozoic crustal accretion in the SW USA is presented. Five Early Proterozoic predominantly volcanic supracrustal terranes are recognized, with ages of 1760-1800 Ma, 1730-1740 Ma, 1720 Ma, 1680-1700 Ma, and 1650 Ma. In some areas they are overlain by a 6th, comprised chiefly of quartzite-pelite. The 1760-1800 Ma terrane appears to reflect a succession of oceanic arcs rapidly accreted to the Archean Wyoming province from the SE, while the 1730-1740 Ma terrane is a back-arc basin formed within the 1760-1800 Ma terrane. The 1720 terrane is interpreted as an evolved back-arc basin in which depleted mantle is tapped. The 1680-1700 Ma and 1650 Ma terranes are remnants of an extensive continental-margin arc system and associated back-arc basins.-from Author