Geon 12 crustal extension in the central Grenville Province, implications for the orogenic architecture, and potential influence on the emplacement of anorthosites

Abstract

Remnants of a ca. 1.24 Ga old volcanic belt formed in a within-plate setting (Manicouagan Crustal Extension Belt) are exposed over several tens of kilometres in the hinterland of the central Grenville Province, and can be recognized despite granulite-facies Grenvillian metamorphism and deformation. This belt mainly consists of layered felsic–mafic rock units, some of which are documented here for the first time. In the vicinity of the 1.24 Ga belt, a Geon 14 arc-related mafic suite and a Geon 15 metasedimentary package were pervasively injected by felsic (and mafic) material, show evidence of a Geon 12 thermal event, and therefore may represent remnants of rifted crust. Following Geon 12 crustal extension, lithospheric-scale magmatic activity in the immediate region continued intermittently, producing mafic dykes at 1.17 Ga and anorthosite at 1.16 and 1.05 Ga. A close association to 1.16 Ga or younger anorthosite is conspicuous to several Geon 12 rock units known in the central and eastern Grenville Province. We therefore suggest that subsequent anorthositic magmatism was focused on zones of lithospheric weakness inherited from Geon 12 crustal extension and remained active intermittently until the end of the Grenvillian orogeny.