Thermal state of northwest Kyushu mantle suggested by the petrochemistry of the Tara-dake basalts

Temperatures of northwest Kyushu mantle are estimated using petrochemical data of the relatively primitive Tara-dake basalts erupted at around 1 Ma. Model primitive melt compositions estimated by the addition of equilibrated olivines to bulk compositions indicate that melting temperatures range from 1230 to 1300degreesC at around 1 GPa. Moderately high melting temperatures of the Taradake basalts indicate that mantle upwelling in NW Kyushu is caused not by thermal plumes but by the convection at the boundary between the continent and the ocean.