Submarine volcanic chain as an indicator of long distance lateral magma transport at oceanic island arc volcano

Abstract:

Recent geophysical observations in the Izu-Bonin intra-oceanic island arc indicate that long-distance lateral magma transport away from volcanic centres is a common volcanic process (e.g., Miyakejima 2000). We report on recent investigations into the magmatic plumbing of basaltic volcanoes of this arc with a special emphasis on lateral magma transport recorded by extensive formation of submarine volcanic chains.

Izu-Oshima volcano is a basaltic volcano in the northern Izu-Bonin arc, and is characterized by numerous, subparallel NW-SE trending submarine ridges extending > 20km to the NW and the SE from the central vent. Submersible survey revealed that these ridges are fissures and chains of volcanoes which erupted basaltic spatter and lava flows. Magma erupted from each ridge shows consistent geochemistry along its length, but has experienced some crystal fractionation and plagioclase accumulation. Compositions of the ridges are also similar to lavas from the subaerial cones that can be traced down the flanks of Izu-Oshima. This is in sharp contrast with the case of Hachijojima volcano, another basaltic volcano in the Izu-Bonin arc, where submarine ridges erupted more primitive magma than subaerial satellite cones (Ishizuka et al., 2008). Submarine ridges of Izu-Oshima show geochemical differences between ridges. Systematic dating and geochemical analysis of subaerial effusives revealed that Izu-Oshima experienced systematic temporal variation of magma chemistry during the last 12,000 years (Ishizuka et al., 2015). Combined with geochemical correlation between the submarine and subaerial vents, each ridge is supposed to record lateral magma transport of different ages. Pairs of subaerial cones and submarine ridges represent the locus of magma transport events away from the reservoir beneath Izu-Oshima. Hence, magma from this crustal reservoir, after being affected by crystal fractionation and crystal accumulation, moved upwards to feed the on-edifice subaerial cones, as well as laterally to supply submarine fissures and dykes. On the other hand, more primitive character of submarine ridges of Hachijojima volcano seems to indicate that the submarine ridges of this volcano represent lateral magma transport at middle to lower crust level before being modified at shallower reservoir.