Trace elements and Nd-Sr isotopes of island arc tholeiites from frontal arc of northeast Japan

On the basis of trace element abundances and Sr and Nd isotope ratios, Quaternary island arc low-alkali tholeiites (IAT) in Northeast Japan are divided into two types: U(undepleted)- and D(depleted)-IAT. U-IAT are characterized by high and constant abundances of Large Ion Lithophile Elements (LILE), which are 10-20 times higher than the primitive mantle value. It is argued that U-IAT magmas were derived by 5-10% batch partial melting of the primitive mantle. D-IAT are characterized by convex-upward patterns with a maximum normalized value for an alkaline earth element in a primitive mantle versus ionic radii(NPR) abundance diagram. D-IAT magmas are considered to have formed in two stages consisting of a depletion in LILE and Nb due to a loss of an extremely small amount of melt (<1%), about 1 Ga from a primitive mantle, and more recently followed by 5-10% partial melting episode under the conditions of formations typical of the U-IAT magmas. -from Authors