NEOARCHEAN ARC MAGMATISM AND SUBSEQUENT COLLISIONAL DEFORMATION ALONG THE EASTERN RAE DOMAIN, WESTERN CHURCHILL PROVINCE, CANADA

The degree to which modern tectonic processes were active in the Archean is an on-going question. 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. Therefore, it is an ideal location to evaluate the tectonic context of an active Archean continental margin. Circa 2.65-2.60 Ga plutonic rocks range from 58.01 to 73.71 SiO₂, and vary from ferroan to magnesian. They form linear trends on modified alkali-lime index, plotting largely in the calc-alkaline field and define a shallow slope of increasing K₂O+Na₂O-CaO with increasing SiO₂. On Pearce 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. These data suggest derivation from a subduction-altered, metasomatized, lithospheric mantle, and as such, the plutonic complex is interpreted to represent the roots of a large arc batholith. Regionally extensive in-situ U-Th-total Pb monazite geochronology, paired with thermodynamic modeling and structural analysis, demonstrate that, following arc-related plutonism, the region underwent pervasive high P granulite facies deformation and metamorphism from ca. 2.59 – 2.54 Ga. At peak metamorphic conditions, the region underwent widespread syn-deformational anatexis at conditions exceeding 1.3 GPa and 800°C associated with pervasive lower crustal flow. The Neoarchean history of the Athabasca granulite terrane, thus, records a phase of arc construction followed by a period of crustal thickening, high pressure granulite facies metamorphism and migmitization, and subsequent relaxation. We interpret this sequence of magmatic, deformational, and anatectic processes to reflect the transition from a continental arc to a collisional tectonic setting. These data support an important component of horizontal tectonics during continental magmatism and accretion in the Neoarchean, and suggest that these lower crustal exposures provide a view of the deeper parts of modern collisional orogens.