Sm-Nd isotopic study on mafic volcanic rocks from the Rankin Inlet and Tavani regions, District of Keewatin, Northwest Territories

Abstract

Sm-Nd isotopic compositions are presented on eleven Late Archean mafic volcanic whole rock samples of the Rankin Inlet and Tavani areas of the eastern Rankin-Ennadai greenstone belt. Three samples from the lower volcanic cycle of the Rankin Inlet Group yielded eNd(2.66 Ga) values of -1.1 to +1.6, and 147Sm/144Nd ratios from 0.1289 to 0.1410, suggesting interaction of the mafic magmas with an older LREE-enriched crustal contaminant. Rocks of the upper volcanic cycle yielded eNd(2.66 Ga) values of +1.8 to +4.5 and 147Sm/144Nd ratios of 0.1374 to 0.1999, and are relatively uncontaminated compared to the lower volcanic cycle. The presence of crustally contaminated volcanic rocks in the lower volcanic cycle indicates that it may have been underlain by older continental-type basement rocks, or that its mantle source was contaminated with crustally-derived fluids or sediments. Four samples from the Tavani area have eNd(2.68 Ga) values of +2.1 to +3.4, indicating derivation from depleted mantle sources, with no obvious interaction with older LREE-enriched crust. One of the five samples from the Tavani area yielded a eNd(2.68 Ga) value of +0.6, raising the possibility of minor contamination from an older crustal component.