11:15 AM - 11:30 AM
[SCG64-24] New insights into the oceanic lithosphere from petit-spot around the Marcus Island
Keywords:alkali-basalt, petit-spot, Pacific, lithosphere, Marcus Island
Clusters of small conical volcanoes occur in the area southeast of Marcus Island, as inferred from precise bathymetric data acquired by the Japan Coast Guard. Most of the cones in the clusters are 〜100 m high and £10 km across. Their morphologies are similar to those of petit-spot volcanoes. A search for petit-spot volcanoes around Marcus Island was conducted in May 2010 by the R/V Yokosuka of JAMSTEC (cruise YK10-05), carrying the submersible Shinkai6500. A young volcano was observed southeast of Marcus Island, contradicting the assumption that Cretaceous seamounts only occur on the Jurassic Pacific plate. The occurrence of highly vesicular alkaline lavas indicates that petit-spot volcanic activity is ubiquitous on the oldest oceanic plate as well. The morphologies of the lava flows in the area southeast of Marcus Island are different to those of flows in the NW Pacific, indicating a low-viscosity magma. The eruption setting in the area southeast of Marcus Island is unusual because the site is located far from any trench. An as-yet unknown origin of petit-spot melt ascending through the lithosphere might be identified via studies of the oldest oceanic crust in the world′s oceans.