Neoarchean arc magmatism and subsequent collisional orogenesis along the eastern Rae domain, western Churchill Province: Implications for the early growth of Laurentia

Abstract

The Athabasca granulite terrane, on the eastern margin of the Rae domain of the western Churchill Province, contains a well exposed record of Neoarchean magmatism, deformation, and metamorphism. Circa 2.63–2.60Ga plutonic rocks range from 58.01 to 73.71 SiO2, and vary from ferroan to magnesian. They form shallow linear trends on modified alkali-lime index diagram, plotting largely in the calc-alkaline field. On tectonic discrimination diagrams, all samples plot in the volcanic arc field. Samples are LREE enriched, and contain relatively steep negative slopes, and flat, depleted, HREE profiles when normalized to chondrites. The entire Neoarchean plutonic complex, independent of lithology, contains strong enrichments in the LILEs and Pb, and depletions in HFSEs. Monazite U-Th-total Pb results from a migmatitic paragneiss suggest that partial melting occurred at ca. 2.57Ga within the Chipman subdomain. Monazite results from the adjacent northwestern subdomain suggest that deformation occurred at ca. 2.57Ga. IN-SIMS and ICP-MS zircon U-Pb geochronology corroborates these conclusions. Although the region is dominated by Paleoproterozoic localized shear zones, internal to each subdomain is evidence of a widespread tectonothermal event during the Neoarchean that involved arc plutonism, crustal thickening, lower crustal flow at pressures exceeding 1.0GPa, and extensive partial melting of the lower continental crust. We interpret this sequence of magmatic, deformational, and anatectic processes to reflect the transition from a continental arc to a collisional tectonic setting. The recognized series of events presented herein is likely correlative to the 2.60–2.50Ga MacQuoid Orogen, which has been recognized further to the northeast, and likely parallels the eastern margin of the Rae domain of the western Churchill Province. These data support an important component of modern style plate tectonics during continental magmatism and accretion in the Neoarchean.