Sr-Nd-Pb Isotope Systematics of Proto-Arc Volcanic Rocks in the Oman Ophiolite

Abstract

Volcanic rocks of the Oman ophiolite include boninite, which is known to represent typical product of proto-arc magmatism. Thus, geochemical characteristics of such boninites and related volcanic rocks have a key to understanding slab-mantle interactions during subduction initiation. In this study, we present Sr, Nd, and Pb isotope compositions of Oman boninites and proto-arc tholeiites extruded prior to the boninites. The proto-arc tholeiites show isotope compositions consistent with melting of mantle metasomatized by slab fluids. On the other hand, boninite compositions require involvement of small amounts of slab melt as well as slab fluids. These isotope variations suggest involvement of hotter slab in boninite magma genesis than in proto-arc tholeiites, probably due to successive subduction of the slab after subduction initiation.