LATE ARCHEAN EVOLUTION OF THE NAIN-PROVINCE, NAIN, LABRADOR - IMPRINTOF A COLLISION

Archean gneisses of the Nain Province in the Nain area, Labrador, comp rise narrow septa between intrusions of the Mesoproterozoic Nain Pluto nic Suite. This region occupies a critical position between the northe rn (Saglek) and southern (Hopedale) blocks of the Nain Province, which experienced distinct thermotectonic histories until the late Archean. Field and geochronological evidence are indicative of a strong late A rchean thermotectonic overprint that is absent from most of the remain der of the Nain Province. Archean gneisses were intruded by granites a nd mafic dykes at 2578 +/- 3 and 2559(-8)(+10) Ma, respectively, and s ubsequently subjected to amphibolite- to granulite-facies regional met amorphism and ductile shearing at ca. 2550 Ma; granite veins and dykes related to the Nain Plutonic Suite were emplaced at ca. 1310 Ma. The Archean events are interpreted to represent the juxtapositioning and f inal docking of Saglek and Hopedale blocks to form a single, stable cr atonic mass during the late Archean. Corroborative evidence indicates that the collisional boundary zone could extend at least 200 km to the north and 150 km to the south of Nain. This late Archean junction may have subsequently been exploited by several Paleoproterozoic granitic intrusions and some members of the Mesoproterozoic Nain Plutonic Suit e.