New geological investigations in eastern Disko: redeposited volcanoclastic sediments with rhyolite from the Nordfjord Member

Abstract

During field work in 1988 in eastern Disko we encountered redeposited volcanoclastic sediments with acid rocks at several localities between Rensdyrdalen and Charles Polaris Dal within lava sequences from the Nordfjord Member of the Maligât Formation. Some of the sediments were only observed during helicopter reconnaissance of steep inaccessible walls and corries, while other sites provided detailed information and samples through field visits. Fig.1 shows the area with newly discovered acid volcanic rocks in eastern Disko. Localities 1 and 2 denote localities investigated in some detail. In north-western Disko peraluminous rhyolite tuffs and conglomerates with almandine-bearing rhyolite blocks occur as widespread but minor deposits in the Nordfjord Member (Pedersen, 1977; Hansen & Pedersen, 1985; Pedersen & Pedersen, 1987). The acid rocks contain graphite and scarce sediment xenoliths and they are associated with contaminated basalts, andesites and dacites, same af which carry nativc iran. The distribution af airfall rhyolite tuff shows that the aciel rocks were erupted somewhere in north-western Disko or in the present shallow sea west af this arca. No eruption sites are exposed at present.