GEOCHEMISTRY OF LATE PROTEROZOIC BASALTIC ROCKS FROM SOUTHEASTERN CAPE-BRETON-ISLAND, NOVA-SCOTIA

Late Proterozoic volcanic rocks of the Fourchu Group from the Avalon Zone in southeastern Cape Breton Island, are composed predominantly of mafic and felsic types with subordinate intermediate units that were all affected by subgreenschist- to greenschist-facies metamorphism. The rocks crop out in four fault blocks and have geochemical characteristics of ensialic orogenic volcanic suites. The basaltic rocks range from tholeiitic to calc-alkaline and show a distinct compositional zonation that resembles the across-arc variation observed in recent volcanic-arc systems. The zonation may be explained in terms of a northwesterly-dipping subduction zone, with the trench lying to the southeast of Nova Scotia. -from Authors