ISOTOPE AND TRACE-ELEMENT GEOCHEMISTRY OF PROTEROZOIC NATKUSIAK FLOODBASALTS FROM THE NORTHWESTERN CANADIAN SHIELD

The Proterozoic continental tholeiites of Natkusiak province (723 Ma o ld) of the northwestern Canadian Shield are part of the Franklin magma tic event. They resemble Phanerozoic flood basalts in their incompatib le trace-element and Sr-Nd-Pb isotopic variations as well as in their large volumes, and a relatively short period of eruption. The wide var iations in Sr-Nd-Pb isotopic and incompatible trace-element ratios (e. g., initial epsilon(Nd) = -5.6 to +5.7) in the Natkusiak basalts, toge ther with the correlations between the isotopic and trace-element rati os, imply the involvement of a crustal component in their genesis. The Natkusiak basalts are inferred to be derived from the subcontinental upper mantle and contaminated by Precambrian basement during their asc ent.