Geochemistry of the Archean Kam Group, Yellowknife greenstone belt, Slave Province, Canada

The geochemistry and isotope systematics of Archean greenstone belts provid e important constraints on the origin of the volcanic rocks and tectonic mo dels for the evolution of Archean cratons. The Kam Group is a similar to 10 -km-thick pile of submarine, tholeiitic mafic, and subordinate felsic volca nic rocks erupted between 2712 and 2701 Ma that forms the bulk of the Yello wknife greenstone belt in the dominantly granite-metasedimentary Slave Prov ince. Mafic rocks range from Normal-mid-ocean range basalt-like basalts to slightly Light-rare-earth-element-enriched (LREE-enriched) but Nb-depleted basaltic andesites and andesites, whereas dacitic to rhyodacitic felsic roc ks are strongly LREE-enriched and highly depleted in Nb. The epsilon(Nd)(T) range from +5 to -3 in the mafic to intermediate rocks and from 0 to -5.5 in the felsic rocks. The epsilon(Nd)(T) decreases with increasing La/Sm, Si O2 and decreasing Nb/La, suggesting that as the mafic magmas evolved they w ere contaminated by older basement rocks. Gneissic granitoids >2.9 Ga in ag e, found at the base of the Kam Group, have epsilon(Nd)(T) between -6 and - 9 and are excellent candidates for the contaminant. The geochemical and iso topic data, combined with the submarine eruptive setting and field evidence for existing continental basement, support a continental margin rift model for the Kam Group. Similar geochemical-isotopic studies are required on ot her Slave greenstone belts in order to test evolutionary models for the Sla ve Province.