TECTONICS OF WSW RAE CRATON OF LAURENTIA; EVIDENCE FOR CRUSTAL ASSEMBLY BY COLLISIONAL, ACCRETIONARY PROCESSES FROM THE MID-NEOARCHEAN TO EARLY PALEOPROTEROZOIC

While the Archean to early Paleoproterozoic transition is a significant turning point in earth history, related tectonic processes remain controversial. The WSW margin of the Rae craton preserves robust evidence for crustal assembly through subduction-related accretion over a large portion of this time interval. In this region, older elements of the Rae craton in the north (Nolan domain) are intruded by an extensive ca. 2.6 granite suite, and bounded to the south by an external (Zemlak) domain, comprising ca. 2.52 and 2.33 Ga orthogneisses within Paleo-Mesoarchean crust; which collectively represent the Taltson basement complex (TBC). The ca. 2.64-2.58 Ga Rae-affinity Nolan granites have subduction-related geochemical signatures and are similar to granites of arc affinity in the Tantato domain to the east. The ca. 2.52 Ga TBC-focused diorite-granodiorite suite, also arc-related, is prevalent along the northern margin of Zemlak domain, next to the Nolan-Zemlak domain boundary, and marks the earliest stages of 2.5-2.3 Ga Arrowsmith orogeny. Neoarchean magmatism is inferred to have begun with subduction below the proto-Rae cratonic core. The presence of older granitoids indicates that subduction initiated at 2.7-2.68 Ga and culminated with widespread granite intrusion at 2.64-2.58 Ga. This was followed by a polarity reversal with younger (≤ 2.56 Ga) arc-style magmatism below an outboard ca. 3.0 Ga terrane now embedded in the TBC. Accretion of this older crustal block across the Nolan-Zemlak domain boundary sometime before ca. 2.52 Ga caused slab failure and emplacement of diorite-granodiorites along the putative early-Arrowsmith suture zone. The continuing magmatic record indicates that thereafter subduction stepped outward leading to a second Arrowsmith-related accretionary event (ca. 2.45-2.4 Ga?), likely docking of the Buffalo Head terrane. The resulting ca. 2.37 Ga metamorphic culmination was followed by emplacement of ca. 2.3 Ga post-collisional granites and Murmac Bay group (2.33-2.0 Ga) deposition. Paleo-Mesoarchean crust of the TBC tracks along the southern and western margins of Rae to the Queen Maud Block in the north. The early-Arrowsmith (2.56-2.52 Ga) suture can thus be traced regionally while a potential late-Arrowsmith suture (ca. 2.45 Ga) in the WSW Rae is concealed below Phanerozoic cover.