GROWTH AND EVOLUTION OF ARCHEAN AND PROTEROZOIC LITHOSPHERE IN MIDDLE LAURENTIA

The upper Great Lakes region preserves a unique record of continental construction and destruction along the southern margin of the Canadian Shield. At about 2.2 Ga plume-related rifting of a Neoarchean (super?)continent resulted in an embayed continental margin which was transformed into a multi-accretionary orogenic belt from 1.9-1.6 Ga. The architecture of the rifted margin likely played an important role in the preservation of subsequent accretion and magmatic events. Newly accreted juvenile Penokean crust was variably metamorphosed, intruded, and deformed by succeeding accretion of Yavapai and Mazatzal arcs. Early sutures were over-steepened during continued arc growth and then modified by subsequent magmatism. A five state aeromagnetic-compilation was used to develop a tectonic province map as well as advance a new geologic interpretation for the Precambrian subcrop. The map construction was greatly aided by several hundred basement-penetrating drill holes and significant new geochronologic data. Using these compilations, we recognize new terrane boundaries that are analogous to Proterozoic sutures in the western U.S. (Cheyenne Belt; Jemez Lineament). Crustal imaging across the readily accessible upper Great Lakes region will enable us to contrast Archean and Proterozoic crustal architecture and evaluate the similarities of their accretionary processes. Also, we can investigate the nature of the Archean tectosphere/Proterozoic lithosphere boundary and learn how different crust and mantle lithospheric types were modified structurally and magmatically beneath the 1.1 Ga Midcontinent rift. EarthScope's USArray and complementary efforts will provide important information on the nature of the transitions between Paleoproterozoic accreted terranes and the affects of the extensive Mesoproterozoic granite-rhyolite magmatism to the south. This region preserves an unmodified record of Archean crustal growth, continental breakup and Proterozoic amalgamation, followed by stabilization, and aborted break-up of Laurentia from 3.6-1.1 Ga. Thus, the geophysical framework of the northern U.S. midcontinent will serve as a template for interpreting how the Laurentian continental lithosphere has been modified by Phanerozoic tectonism and magmatism in the eastern and western U.S.