Metavolcanic Rocks of the La Ronge Domain in the Churchill Province, Saskatchewan: Geochemical Evidence for a Volcanic Arc Origin

Abstract

Summary The La Ronge Domain in the Churchill Province of the Canadian Shield is a volcanic-sedimentary-plutonic belt of early Proterozoic age. Geochemical data, supported by geological evidence, strongly suggest that the La Ronge metavolcanics were emplaced in an island arc setting. The metavolcanic rocks range from basalt through andesite to dacite and rhyolite. Calcalkaline and tholeiitic types are dominant, with minor alkaline varieties. Classification based on the major elements produces ambiguous results because of mobility of these elements during metamorphism. However, relatively immobile, minor and trace elements provide reliable characterization, of the basalts in particular. The latter display distinctive trace element properties and MORB-normalized geochemical patterns similar to those of recent volcanic arc basalts, being enriched in incompatible elements of low ionic potential and depleted in those of high ionic potential. The calcalkaline basalts are, in addition, enriched in Th, P, Ce and Sm. A minor within-plate component is also displayed by some metabasalts, suggesting that magma genesis in parts of the La Ronge ‘arc’ involved sub-continental lithosphere. Rare earth element patterns show enrichment in the LREE with little or no Eu anomaly. Interpretation by means of trace element discrimination diagrams (incorporating elements such as Ti, Y, Nb, Zr, Cr, Th, Yb and Ce) provides clear evidence for emplacement in a volcanic arc tectonic setting.