Paleo- to Mesoarchean basement recycling and terrane definition in the Northeastern Superior Province, Québec, Canada

Abstract

The Northeastern Superior Province (NESP) is a 500 km × 700 km segment of plutonic Archean crust generated by 1.2 Ga of tectonomagmatic activity. The NESP exhibits the classical plutonic series of Archean terranes, low-K tonalite–trondhjemite–granodiorite (TTG) and high-K granodiorite–granite–monzogranite (GGM) with unusually large volumes of Px-TTGs (mostly enderbites and subordinate charnockites). Volcanic rocks constitute <10% of the NESP and are dominated by magnesian basalt-komatiite assemblages and bimodal mafic tholeiitic and calc-alkaline felsic tuffs. Mapping, U/Pb geochronological, and Nd isotopic data suggest the presence of two terranes with distinct magmatic histories: the Hudson Bay to the SW, and the Rivière Arnaud to the NE. These terranes are separated by a metasedimentary basin, which may be a paleosuture. The Hudson Bay terrane is a Paleo- to Mesoarchean TTG-greenstone craton (3.8–2.9 Ga), intruded by 2.76–2.74 Ga low-K TTGs and younger 2.72–2.69 Ga high-K GGM and Px-TTGs that have low Nd isotopic values (ɛNd T = +0.45 to −5.03). Mafic to felsic volcanic rocks and mafic to ultramafic plutonic rocks <2.76 Ga also have enriched ɛNd T = +0.40 to −6.90. These radiogenic signatures (as well as inherited zircon cores) record recycling of Mesoarchean (3.8–2.9 Ga) crust, either through direct melting, or by coupled assimilation-fractional crystallization processes. In comparison, the Rivière Arnaud terrane is underlain by younger (<3.0 Ga), more juvenile TTG crust, that is intruded by plutons of low-K TTGs (2.79–2.76 Ga), high-K GGM (2.73–2.72 Ga), and Px-TTGs (2.74–2.72 Ga). Most of these rocks have positive to moderately negative ɛNd T values (+2.34 to −0.67), indicating either a juvenile character, or recycling of fairly juvenile Late Mesoarchean-Early Neoarchean crust. Overall, geochemical and isotopic data of the Late Neoarchean (<2.76 Ga) low-K TTG and Px-TTG series of the NE Superior Province are not consistent with partial melting solely of juvenile basaltic crust in an oceanic setting. The data are most consistent with remelting of a composite crust constituted of older, isotopically enriched mafic–ultramafic rocks and more juvenile metabasaltic rocks. The basaltic component may have been introduced either by crustal underplating, intra-plating or foundering of supracrustal belts. The mafic melts injected into the maturing cratonic nuclei assimilated the older rocks by an AFC-type process and provided heat. The isotopic and geochemical data imply that the high-K GGM series melts were produced by melting at shallower depth of an older composite TTG crust, with less involvement of the metabasaltic component.