During the DELP ’85 Cruise we observed following evidence for the presence of a Quaternary volcano in southeast margin of the Japan Basin. The station is located at 40°42’N latitude, and 139°03’E longitude at a depth of 3320 m, which is about 100 km northwest of Ichinomegata volcano of the northeast Japan arc. (1) Anomalous reflection was recorded up to about 75 m above sea bottom by a 3.5 kHz echo sounding system, which may represent either reflection from gas bubbles or solid fragments rising from a vent. A small (less than 200 m in diameter) basin structure was recorded just below the anomalous reflection. (2) High heat flow of ca. 250 mW/m^2 was obtained at the station. (3) We recovered rather fresh volcanic sand, consisting mostly of glassy fragments of basalt through rhyolite, and crystals of olivine, augite, hornblende, biotite, opaque mineral and plagioclase. These fragments conform a suite of island-arc alkalic rocks. The glasses have the highest alkali content among Quaternary volcanic rocks of the northeast Japan arc. Mineralogically and chemically, the volcanic sand is not correlated to heretofore known volcanic products around Japan. It is most probable that a Quaternary volcano is present near the station.
