A U-PB GEOCHRONOLOGICAL FRAMEWORK FOR THE PINWARE TERRANE, GRENVILLE PROVINCE, SOUTHEAST LABRADOR

The Pinware terrane in the eastern Grenville Province of Labrador is c haracterized by abundant granitoid rocks but a lack of metasedimentary gneiss. On the basis of newly obtained U-Pb zircon ages, the followin g history is outline Supracrustal rocks, including felsic volcanics, w ere formed at 1640 +/- 7 Ma. These rocks were migmatized and injected by mafic dikes, prior to being included as enclaves in a quartz monzon ite emplaced at 1490 +/- 5 Ma. This quartz monzonite and two other gra nitoids dated at 1479 +/- 2 and 1472 +/- 3 Ma belong to a newly identi fied, regionally extensive 1500-1470 Ma event to which the name Pinwar ian is assigned. In an eastern Laurentia-Baltica context, the Pinwaria n event is interpreted to be part of Middle Proterozoic crustal activi ty. Subsequent mafic dike and pegmatite injection may correlate with e mplacement of granitoid rocks at ca. 1145 Ma. Two deformational events followed; the second event is dated at 1000 +/- 2 Ma on the basis of metamorphic zircon from a mafic dike. Previously identified post-tecto nic 966-956 Ma granitoid magmatism is confirmed by 960 +/- 2 and 959 /- 2 Ma intrusive ages and a ca. 964 Ma lower-intercept age from a Pin warian quartz monzonite.