Geochemistry of Basalt from the Eastern Woodlark Basin: Its Implications for the Mantle Heterogeneity

Abstract

A section of the active spreading center in the eastern Woodlark Basin (EWLB) is subducting beneath the New Georgia Group, a volcanic arc. Basalt from the axis of EWLB were analyzed to investigate the processes in the region where ridge subduction and reversal in subduction polarity occurred in the past. They are similar to N-MORB in their major oxides, but are more depleted in incompatible elements. Incompatible element ratios such as Zr/Y and La/Sm show a large variation, which may be explained by mantle heterogeneity where an N-MORB source became mixed with or coexists with a different, mantle source that was depleted at an earlier time. The negative correlation between Ba/La and Zr/Y ratios indicates that the prior depleted end member is more enriched in the subduction component than the N-MORB mantle source and therefore may have originated from a subduction environment. The source of the subduction component remains to be explored by further studies.