Rock fragments and pebbles dredged near Jimmu Seamount, northwestern Pacific

Abstract

Fifty-five rock fragments and pebbles were dredged at 2,550–2,800 fathoms (4,650–5,100 metres) near Jimmu Seamount, 700 miles southeast of Kamchatka. Tuffaceous shale, andesitic and dacitic tuff, pyroxene-hornblende dacite-pumice, and augite-hypersthene andesite are the most abundant rock types. Minor constituents in the haul include augite-pigeonite basalt, augite-olivine basalt, olivine dolerite, quartz syenite porphyry, metabasalt, sandstone, and chert. Petrographic and chemical analyses indicate closer affinities with Kuril Islands and Kamchatka volcanic rocks than with Cenozoic Japanese or Pacific Basin types. Probably these rocks were dropped by Pleistocene icebergs carried south and east by ocean currents.