Paleoproterozoic lithotectonic divisions of the southeastern Churchill Province, western Labrador

Abstract

The southeastern Churchill Province (SECP) is a Paleoproterozoic system of orogens that formed during collision of the Nain and Superior cratons with a composite lithotectonic terrane that now forms the medial, metamorphic–plutonic core zone of the SECP. In western Labrador, the core zone consists of reworked Archean gneisses, Paleoproterozoic supracrustal rocks, and variably deformed 1.83–1.81 Ga granitic plutons. It is subdivided into three Paleoproterozoic lithotectonic domains (McKenzie River, Crossroads, and Orma), which are separated from each other by dextral transpressive high-strain zones. Crossroads and Orma domains are thought to be derived from Archean high-grade granite–greenstone terrane crust, whereas McKenzie River domain is inferred to have been part of an Archean orthogneiss terrane dominated by the ca. 2776 Ma Flat Point gneiss. U–Pb geochronological data indicate that the igneous precursor of the Flat Point gneiss is >80 Ma older than the oldest tonalité–granite intrusions in Crossroads and Orma domains. The three domains were variably reworked during dextral oblique convergence of the Superior and Rae cratons. Field and geochronological data demonstrate that in McKenzie River and Crossroads domains, 1.83–1.80 Ga tectono-thermal reworking included medium- to high-grade metamorphism and the formation of north-trending structures and regionally persistent high-strain zones. Crossroads domain also contains a significant amount of 1.83–1.81 Ga granitic intrusions, including the southern part of the 500 km long De Pas batholith. Orma domain appears to have escaped Paleoproterozoic metamorphism and deformation, suggesting that a "Hudsonian" tectono-thermal front separates it from Crossroads and McKenzie River domains.