Geochemical constraints on mantle source nature and recycling of subducted sediments in the Sulu Sea

Abstract

The Sulu Sea is a marginal spreading basin in the triple junction of Euro-Asia/Indian/Pacific plates. The genesis of seafloor basalts is crucial for understanding the nature and evolution history of the underlying mantle in this region. Nevertheless, the mantle source of the Sulu Sea remains unclear due to limited geochemical data. In this study, we report a complete set of whole-rock major and trace elements and Sr-Nd-Pb-Hf isotopes for the volcanic rocks at Ocean Drilling Program Site U768 in the Southeast Sulu Sea. These volcanic rock samples are characterized by transitional trace element compositions between mid-ocean ridge basalts (MORBs) and island arc basalts (IABs). A subduction modified depleted mantle source is indicated by their higher Th/Yb ratios than the MORB-OIB array and trace element patterns. We propose that the pelagic sediments contributed to the mantle source of the Southeast Sulu Sea based on the plots of ²⁰⁶Pb/ ²⁰⁴Pb vs. Ce/Pb and Th/Nb. Based on the decoupled Hf–Nd isotopes and the variation of Pb isotopes for Site U768 volcanic rocks, we suggest that subducted pelagic sediments contributed to the origin of the Indian-type mantle of the Southeast Sulu Sea.