DISTRIBUTION AND CHARACTER OF LATE PALEO- TO EARLY NEOPROTEROZOIC ROCKS IN THE CANADIAN COMPONENT OF RODINIA

Pre-Grenvillian Laurentia (PGL) was established as a major continental block by the end of the Paleoproterozoic (1.6 Ga). Continental sedimentary cover of exhumed Archean and Paleoproterozoic orogenic rocks spanning this time boundary (Athabaska, Thelon, Hornby Bay) have continental character, were probably connected, and may once have covered much of PGL; coeval rocks along the present western margin (Wernicke, Musqua) have passive margin attributes. Continental to shelf-type character is maintained by early to mid-Mesoproterozoic groups (Sibley, Dismal Lakes-Coppermine, Bylot, Fury and Hecla, Sims), some accompanied by continental flood basalt related to extensive diabase dyke swarms; other magmatic activity during this time is restricted to small, widely scattered, generally alkalic intrusions, with the exception of voluminous anorogenic anorthosite and related granitoid magmatism in Labrador–NE Quebec, itself coeval with anorthosite and granite-rhyolite magmatism in midcontinental USA. The Belt-Purcell at the W margin appears to have a provenance other than PGL. The Grenville Province along the present SE margin of PGL resulted from compressive tectonics presumed to have been related to the assembly of Rodinia. Composed mainly of reworked PGL crust, in places once doubled in thickness, it preserves an early Mesoproterozoic history (1.5–1.35 Ga) of continental magmatic arc activity (Pinware, Wakeham, Britt). Also preserved are remnants of volcanic arc and back-arc deposits (Montauban, Grenville), with attendant TTG-suite (1.35–1.23 Ga), that formed mainly on PGL crust but may possibly include obducted rocks from marginal volcanic arcs that preceding terminal continent-continent collision at ca. 1.2 Ga. Post-collisional development of the Midcontinent Rift (1.1 Ga) does not coincide with any major event recorded in the Grenville orogen, although compressive tectonism and plutonism continued there until 1.0–0.95 Ga. Early Neoproterozoic sedimentary rocks in NW Laurentia (Shaler, Mackenzie Mountains) contain Grenvillian detritus, indicating continental bypassing via huge river systems, and mid-Neoproterozoic rift sediments deposited on the exhumed Grenville orogen in Labrador (Double Mer), the W Laurentia margin (basal Windermere), and younger diabase dyke swarms (0.6 Ga) relate to breakup of Rodinia.