Petit-spot volcanoes on the oldest portion of the Pacific plate

The formation of a petit-spot volcano involves the ascent of an asthenospheric melt to the outboard part of a plate subduction zone where flexure of the plate has taken place in the outer trench swell. On the Pacific Plate, the only previously known examples of such volcanoes were in the vicinity of the Japan Trench. We describe here a newly discovered petit-spot submarine volcano that formed in one of the oldest parts of the Pacific Plate among a cluster of small conical knolls to the southeast of Minamitorishima (Marcus) Island. Geochronological data indicate that this petit-spot volcanic eruption occurred less than 3 million years ago. The volcano erupted on the eastern slope of the outer rise, and it is at an unusually large distance from the Mariana trench axis (~800 km) because this rise, near the older part of the Pacific Plate, is wider than those of other subduction systems.