Geochemical and isotopic (Nd-O) evidence bearing on the origin of late- to post-orogenic high-K granitoid rocks in the Western Superior Province: implications for late Archean tectonomagmatic processes

The granitoid rock dominated central Wabigoon subprovince of the Superior Province records low-K trondhjemite-tonalite-granodiorite (TTG) type magmatic episodes at <2.83-2.74 and 2.722-2.709 Ga, and high-K mafic to felsic plutonism at 2.690-2.685 Ga. High-K units consist of granite to granodiorite dykes and sills, a K-feldspar megacrystic granodiorite suite of sanukitoid affinity and a suite of mafic dykes and intrusions. Initial epsilon(Nd) values (-3.1 to +3.3) indicate variable input to all units from light REE-enriched older crustal materials. The delta(18)O (VSMOW) range of felsic compositions (+7.1 to +8.9%) overlaps closely that of average upper Superior Province crust. The granite/granodiorite units probably received melt components derived from both older tonalitic crust and isotopically juvenile supracrustal material. The thermal flux for partial melting was provided by mafic components of the coeval megacrystic granodiorite suite. This latter suite likely formed by extensive crustal assimilation and fractionation of enriched-mantle-derived high-Mg dioritic magmas in a post-collisional setting, possibly resulting from slab breakoff or broader scale lithospheric delamination. A genetic link is inferred between mafic magmatism and the late- to post-tectonic high-K granitoid magmatism that typically represents the last stabilization event within Superior subprovinces. That crustal recycling processes played a major role in the petrogenesis of central Wabigoon high-K granitoid suites is consistent with other evidence that supports repeated and substantial continental recycling within this subprovince as far back as the Mesoarchean. (C) 2004 Elsevier B.V. All rights reserved.