Geochemistry and isotopic composition of volcanic rocks of ODP Hole 128-794D

Two superposed volcanic complexes are distinguished. The upper complex consists of continental tholeiite sills dated around 20-18 Ma and attributed to the rifting stage of the backarc basin.

The lower complex consists of backarc basin basalts probably intruded below the upper complex during the spreading stage. Trace-element compositions and Sr and Nd isotopic signatures may be explained by mixing of at least two end members with a very small addition of crustal and subducted sediment component. Thus, upwelling of mantle diapir occurred during the rifting stage.