Coarse-grained volcanic detritus in deep-sea sediments of the northeastern Equatorial Pacific

Abstract Coarse-grained volcanic detritus in near-surface sediments of the northeastern equatorial Pacific consists mainly of feldspar (plagioclase with An 35–70 Or 0–4 ) and magnetite, with minor parts of pyroxene (augite, Wo 25–32 En 53-32 ) and volcanic quartz. Except for plagioclase (0.005–0.5% of total sediment) all concentrations range between 0 and 30 grains m −1 of piston-core, where differences exist within the stratigraphic sequence and also from mineral to mineral. The following relationships have been found: • —Plagioclase > magnetite >volcanic quartz >pyroxene. • — Contents are low in Plio-Quaternary sediments and in Lower Miocene pure radiolarian ooze. They increase within the Late Eocene to Early Oligocene sediments and near the Early Oligocene hiatus. The morphology, distribution and alteration of the minerals are described and singlegrain analyses for plagioclase and pyroxene are given. The origin of plagioclase, pyroxene and magnetite is related to the formation of new oceanic crust at the East Pacific Ridge. Transport and distribution by slumping, high-density currents and reworking of older sediments are assumed. The origin of volcanic quartz from potential source areas in northern Central America and Western Mexico and transport and accumulation in deepsea sediments are discussed.