SM-ND isotopic studies of proterozoic anorthosites Systematics and implications

Sm-Nd isotopic studies of anorthosites can be used to provide information on their ages of crystallization and metamorphism, contamination history, and mantle sources. Proterozoic anorthosites in the Grenville and Nain Provinces of eastern North America crystallized between about 1100 and 1600 Ma, and some were metamorphosed at about 1000 Ma. Grenville Province anorthosite massifs were derived from depleted mantle. It is not clear whether massifs and related mafic intrusions throughout the Nain Province of Labrador were derived from enriched mantle, or were contaminated by early Archean (greater than 3500 Ma) silicic crustal materials, heretofore thought to be restricted to coastal Labrador.