Age and tectonic implications of Paleoproterozoic granitoid intrusions within the Nain Province near Nain, Labrador

U-Pb (zircon) age determinations from three granitoid intrusions in the Nai n region, formerly assigned to the well-known 1.35-1.29 Ga (Mesoproterozoic ) Nain Plutonic Suite (NPS), indicate that they were emplaced, instead, dur ing the Paleoproterozoic. Crystallization ages of 2109 +/- 3 Ma for Sheet H ill granite, 2052 +/- 4 Ma for Loon Island granite, and 2025 +/- 7 Ma for S atok Island monzonite demonstrate a decreasing time of emplacement from nor th to south. Leucocratic basic rocks, superficially similar to those of the NPS, occur as inclusions within the Satok Island monzonite and are intrude d by an 1873 +/- 4 Ma granitic aplite dyke north of Webb's Bay. The ages cl early demonstrate granitic magmatism in the Nain area for at least 750 Ma, and anorthositic magmatism for at least 675 Ma, before the development of N PS. The earliest Paleoproterozoic magmatism (2109-2025 Ma) may have coincid ed with breakup of the North Atlantic craton, whereas the local magmatism r epresented by the 1873 Ma aplite dyke may be related to the embryonic stage s of the continental collision that produced the 1860-1740 Ma Torngat Oroge n. Leucocratic basic rocks associated with the Paleoproterozoic granitic ro cks identified here could be Archean in age, but are more likely coeval wit h the granites. Other granitic and basic rocks in the Nain area may likewis e be products of this bimodal plutonism. Identification of this possible ge ological duality suggests repetitive magmatism of "anorogenic type" over a significant time span in this part of Labrador. If the mantle-plume-related genesis accorded the Mesoproterozoic NPS is applicable to the Paleoprotero zoic rocks, it implies multiple periods of similar lithosphere-asthenospher e interaction in this area, beginning at least in the Paleoproterozoic. The Paleoproterozoic magmas may have been emplaced into Nain Province crust al ong a linear intracontinental extension zone inboard from a rifted margin.