LATE PRECAMBRIAN ASH-FLOW TUFFS AND ASSOCIATED ROCKS OF THE HARBOR MAIN GROUP NEAR COLLIERS, EASTERN NEWFOUNDLAND - CHEMISTRY AND MAGMATIC AFFINITIES

The Colliers Peninsula, a typical area in the western part of the Harbour Main Group in eastern Newfoundland, is underlain by three steeply-dipping sequences of ash-flow tuffs 250-500m thick, separated by clastic sediments, conformably overlain by subaerial mafic flows and cut by small bodies of high-level intrusive rocks rich in plagioclase phenocrysts. All rocks are of low metamorphic grade. The present composition of the rocks reflects complex chemical adjustments, both contemporaneous with and subsequent to the magmatic event. However, mineralogical and chemical data and trends considered to be a part of the original magmatic heritage are consistent with suggestions that the western (probably lower) part of the Harbour Main volcanic pile was formed in a continental, extensional tectonic environment.