Geochemistry and Petrology of Granitoid rocks of the Gander zone, Bay D'Espoir area, Newfoundland

摘要

Two pulses of granitoid plutonism have been recorded in the Bay D'Espoir area: (1) The Northern Granitoids were intruded discordantly into medium to low grade sedimentary and volcanic rocks of the Bay D'Espoir Group, at ca. 430 Ma. (2) The Southern Granitoids were intruded concordantly into gneisses and migmatites of the Little Passage Gneisses at ca. 350 Ma. Although the granitoids occupy a cross section through the Gander Zone, they do not show any systematic petrographic, geochemical, or isotopic variation from north to south. -- The "Straddling Granite", formerly considered to lie astride the Gander-Avalon Zone boundary, consists of at least two separate plutons on either side of the boundary. Although no economic mineral deposits have yet been discovered, leucogranites with ore-bearing potential occur in sufficient quantity to warrant further investigation. Structural, stratigraphic, geochemical and isotopic evidence suggest that the granitoids were intruded into a back-arc basin during the Acadian Orogeny.