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The Okinawa Trough is an incipient intracontinental back arc basin that has developed behind the Ryukyu arc‐trench system. To explore its magmatic evolution and the nature of the mantle source, we present major and trace element and Sr‐Nd isotopic data for mafic volcanic rocks from the Middle and Southern Okinawa Trough and the Central Ryukyu Arc. Two episodes of activity formed the latter: older (∼21–13 Ma) and younger (∼6–4 Ma). Although Quaternary basalts from the Middle Okinawa Trough (MOT) have major element compositions comparable to basalts from intra‐oceanic back arc basins, they are characterized by relative enrichments of large ion lithophile elements and Pb and by depletions of high field strength elements analogous to those observed in Ryukyu Arc volcanics. Two components have been involved in the generation of MOT basalt, which we identify as an E‐MORB type (or oceanic …