Abstract

The Pinware terrane is located in the easternmost Grenville Province and contains crust of Labradorian (1710–1600 Ma), Pinwarian (1520–1460 Ma), Elsonian (1460–1230 Ma), Grenvillian (1080–985 Ma), and late- to post-Grenvillian (985–955 Ma) age. Newly obtained U–Pb geochronological data enhance understanding of all these evolutionary stages. A Labradorian age of 1632 ± 8 Ma has been obtained for the Brador River granite, thereby establishing the presence of mid- to late- Labradorian rocks in the southernmost part of the region. A maximum age of ∼1600 Ma obtained for the Ten Mile Lake granite indicates for the first time that Labradorian crust could continue into the northern Long Range Inlier of western Newfoundland. Pinwarian activity is indicated by ages of ∼1526–1504, 1500 ± 14, 1467 ± 44, and 1466 ± 8 Ma from granitoid rocks at Rivière St-Paul, West St. Modeste, Diable Bay, and Pinware, respectively. The first evidence for late Elsonian mafic magmatism in this region is provided by a concordant baddeleyite date of 1248 ± 5 Ma from gabbronorite at Lourdes-de-Blanc-Sablon. This study has also identified an early post-tectonic, high-level, mafic–anorthositic–syenitic magmatic event between 985 and 975 Ma. Recognition of the event relies on previous results and newly obtained ages of 979.5 ± 2.8 Ma from the Red Bay gabbro, 974.5 ± 1.8 Ma from the Vieux Fort anorthosite, and 969 ± 11 Ma from the Lower Pinware River alkali-feldspar syenite. Time, composition, and fabric criteria distinguish these rocks from late-post-tectonic monzonite, syenite and granite emplaced between 966 and 956 Ma.

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