U–Pb geochronological constraints for Paleoproterozoic evolution of the Core Zone, southeastern Churchill Province, northeastern Laurentia

Abstract

The Core Zone of the Southeastern Churchill Province, northeastern Laurentia, is a composite of Paleoproterozoic lithotectonic domains assembled in the vise between obliquely colliding Archean Superior and North Atlantic cratons between ca. 1860 and 1810 Ma. Detailed geological and U–Pb geochronological studies of domains in the southern Core Zone highlight significant differences in Archean and Paleoproterozoic geology between domains, and constrain timing and models for Paleoproterozoic assembly. In the south-central part of the Core Zone, Crossroads and Orma domains consist of Late Archean granite–greenstone terrane crust. Crossroads domain also contains a significant number of granite–charnockite intrusions belonging to the 1840–1810 Ma De Pas batholith; magmatism pre-dates and overlaps with ca. 1820–1775 Ma high-grade metamorphism and attendant deformation. In marked contrast, Orma domain, which occurs to the east of Crossroads domain, contains only local evidence of Paleoproterozoic (De Pas related?) intrusions and appears to have mainly escaped Paleoproterozoic metamorphism and penetrative deformation. A model compatible with available data suggests the De Pas batholith is a continental magmatic arc formed above an east-dipping subduction zone. Paleoproterozoic metamorphism and deformation is concentrated in regions contiguous with arc magmatism. West of Crossroads domain, and separated from it by the Lac Tudor shear zone, McKenzie River domain is dominated by Archean orthogneiss (>80 m.y. older than gneisses in Crossroads and Orma domains), minor amounts of Paleoproterozoic supracrustal rocks (absent in domains to the east) and 1815 Ma tonalite. It does not contain De Pas intrusions. U–Pb geochronology suggests juxtaposition of the McKenzie River domain with domains to the east may have occurred around 1810 Ma. One possible model envisages the McKenzie River domain as a piece of reassembled Superior craton crust, incompletely rifted from the Superior margin during ca 2.17 Ga rifting. Domains occurring east of the Lac Tudor shear zone are interpreted to be exotic with respect to the Superior craton.