ABSTRACT: Sr, Nd and Incompatible Element Variations in Back Arc Rocks from the Sumisu Rift in the Izu-Ogasawara Arc: Implication for Tectonic Evolution

Masato Nohara, Brian Taylor, Glenn Brown

Sr and Nd isotope ratios are 0.70317-0.70325 and 0.51286-0.51305, respectively. The Sr vs Nd ratio relations shift toward bulk earth values, suggesting that the Sumisu Rift rocks were formed by mixing of T(N)-type MORBs and island arc-melts. Based on REE and isotope data, the Sumisu Rift is maintained in chemically immature stage, indicating that the Rift is retained in rifting or prespreading stage, which is consistent with the results of ODP Leg 126.