Petrography and mineralogy of volcanogenic sediments from DSDP Leg 48 southwest Rockall Plateau

Quaternary, middle Eocene, lower Eocene and Paleocene volcanogenic sediments were cored at DSDP Leg 48 Sites 403 and 404, on the rifted southwest margin of the Rockall Plateau. The Paleocene-lower Eocene tuffaceous sequence is thickest (140 m) at Site 403, but tuff bands are attenuated and diluted by orthoclastic sediment at Site 404. Site 403 tuffs are mainly of granule, sand-grade, and silt-grade with sparse lapilli. Glass shards are almost entirely argillized, but sparse unaltered shards with pumice and microlitic lava particles indicate mainly basaltic parent magmas with minor rhyolite. The Paleocene-lower Eocene cores indicate a succession of mainly effusive eruptive events, probably originating in the Reykjanes Ridge, Iceland province. Heavy mineral suites group as amphibole-epidote, diopside-hypersthene, and augite-olivine; they are largely unrelated to the pyroclasts and were derived mainly from metamorphic basement including granulites and amphibolites. Vitroclastic foraminiferal ooze of Quaternary age at Site 404 contains abundant fresh glass shards of basaltic and minor rhyolitic types. The record of Paleocene to lower Eocene vulcanism greatly extends the lower Tertiary volcanic province of northwest Europe, the North Sea Basins, Iceland, and Greenland into the northeast Atlantic; and correlates widespread magmatism with rifting and subsidence in the North Sea and the major opening of the North Atlantic.