THE NEORCHEAN RECORD OF THE CANADIAN PRECAMBRIAN SHIELD: NEW PERSPECTIVES FROM THE CRUST AND LITHOSPHERE

The Canadian Precambrian Shield (CPS) is comprised of Archean cratons, numerous microcontinents and crustal slivers, and a lesser volume of juvenile Paleoproterozoic crust within which there is a rich record from the Hadean to the end of the Archean at 2.5 Ga. Major advances in isotopic research, geophysical probing and a new era of northern mapping are bringing to light an increasingly complex mosaic. The CPS is comprised of seven major cratons-Slave, Rae, Hearne, Superior, Nain and buried Mackenzie—and at least a dozen microcontinents, which range from pericratonic following Paleoproterozoic rifting (Hall-Aasiat, Duggan, Kuujuaq), to rifted from their parent supercratons (Superia, Nunavutia) and reassembled (Sask-Partridge Breast, Buffalo Head, George River, Falcoz, Sugluk?). Several exotic blocks are known: the Mesoarchean Chipman domain and Queen Maud block, and the latest Neoarchean Boothia terrane and the buried Wabamun terrane in south-central Canada. A significant subset of the microcontinents were heavily reworked and added to during the Paleoproterozoic and include only fragmentary Neoarchean records (Meta Incognita, Hottah, Mistabini-Raude). The larger cratons such as Slave, Rae, Nain and Superior have distinct internal subdivisions with varying Paleo-Mesoarchean versus Neoarchean parentage reflecting Meso-Neoarchean orogenic activity that assembled these components into their nascent proto-cratons. Geophysical and mantle studies have probed into the Archean deeper crustal and lithospheric architecture revealing patterns of distinct lithosphere composition and seismic grain that mirror the heterogenous crustal record. Xenolith and diamond inclusion dating document significant contributions to the lithosphere during early Paleo-Mesoarchean assembly of the cratons but with a highly variable record of Proterozoic and younger refertilization/growth during Laurentia’s assembly. By the Neoarchean the preceding blocks and new crust were assembled into the major Neoarchean supercratons, with igneous and metamorphic activity in the blocks displaying distinctly provincial patterns at varying times, often in linear zones along block boundaries. Along with substantial evidence for arcs, ocean basins, geophysically imaged subducted plates and plate boundaries, and collisional orogens with prograde Barrovian and peak conditions up to high pressure granulite and eclogite, these temporal-spatial patterns highlight a more modern-like plate tectonic circuit by Neoarchean time.