A U-Pb Geochronological Framework for the Pinware Terrane, Grenville Province, Southeast Labrador

Abstract

The Pinware terrane in the eastern Grenville Province of Labrador is characterized by abundant granitoid rocks but a lack of metasedimentary gneiss. On the basis of newly obtained U-Pb zircon ages, the following history is outlined. Supracrustal rocks, including felsic volcanics, were formed at $$1640 \pm 7 Ma$$. These rocks were migmatized and injected by mafic dikes, prior to being included as enclaves in a quartz monzonite emplaced at $$1490 \pm 5 Ma$$. This quartz monzonite and two other granitoids dated at $$1479 \pm 2$$ and $$1472 \pm 3 Ma$$ belong to a newly identified, regionally extensive 1500-1470 Ma event to which the name Pinwarian is assigned. In an eastern Laurentia-Baltica context, the Pinwarian event is interpreted to be part of Middle Proterozoic crustal activity. Subsequent mafic dike and pegmatite injection may correlate with emplacement of granitoid rocks at ca. 1145 Ma. Two deformational events followed; the second event is dated at $$1000 \pm 2 Ma$$ on the basis of metamorphic zircon from a mafic dike. Previously identified post-tectonic 966-956 Ma granitoid magmatism is confirmed by $$960 \pm 2$$ and $$959 \pm 2$$ Ma intrusive ages and a ca. 964 Ma lower-intercept age from a Pinwarian quartz monzonite.