GEOLOGY ACROSS THE NOLAN-ZEMLAK DOMAIN BOUNDARY, A CRYPTIC EARLY-ARROWSMITH (CA. 2.52 GA) COLLISIONAL SUTURE IN THE WSW RAE CRATON

The Archean-early Paleoproterozoic transition is an important period in earth history, characterized by major crust formation and the emergence of continents. The 2.5 to 2.3 Ga Arrowsmith orogeny, along the western margin of Rae craton of Laurentia, provides insights into tectonic processes within this critical time window. Recent work in the SW Rae has uncovered evidence that Arrowsmith orogenesis involved subduction-related processes across a putative latest Neoarchean collisional suture zone, the highly sheared boundary between the Zemlak and Nolan lithotectonic domains. This boundary marks an abrupt change in geology and structural style, separating weakly deformed 2.64-2.58 Ga granitoid rocks of the Nolan domain to the north, from a prominent suite of ca. 2.52 Ga dioritic-granodioritic gneisses of the Zemlak domain to the south. Both suites have geochemical-isotopic signatures consistent with generation by subduction-related slab failure, but the Zemlak suite is distinguished from the Nolan by its anomalously low Th. In the transition across the domain boundary, the Nolan granites are progressively mylonitized within the ca. 2.37 Ga South Tazin Lake shear zone that straddles the tectonized contact between respective suites. Ductile deformation occurred ca. 2.37 Ga but the Nolan suite also records older ca. 2.52 Ga thermal resetting attributed to intrusion of the Zemlak suite. Regionally, these observations are best explained by subduction-related accretion of an outboard Paleo-Mesoarchean terrane, now embedded in the Zemlak domain (and greater Taltson basement complex (TBC)), to a proto-Rae-cratonic core dominated by 2.6 Ga granitic rocks. Accretion was followed by slab failure, with emplacement of the Zemlak suite along the suture zone and preferentially into the overriding (Zemlak-TBC) plate; the suture is temporally constrained to between 2.56 Ga and 2.52 Ga. Subduction then stepped outward based on the occurrence of younger (<2.52 to 2.3 Ga) granitoids in the TBC to the south and west. The suture zone was reworked under ductile conditions at the peak (ca. 2.37 Ga) of Arrowsmith orogeny and subsequently reactivated in a ductile-brittle regime at 1.93 Ga. Preliminary analysis suggests that this early Arrowsmith-age suture zone is a regionally significant boundary.