Origin of the early Cretaceous Liucheng OIB-type dolerite sill in Zhejiang Province, coastal region of SE China: Implications for recycling of the Paleo-Pacific slab

Abstract

Both early Cretaceous ocean island basalt (OIB)-type and subduction-related arc-type mafic magmatism occurred in coastal region of SE China. However, whether there existed a genetic relationship between the OIB-type magmatism and contemporary subduction of the Paleo-Pacific Ocean remains unclear. Here we present a comprehensive geochemical dataset of the Liucheng dolerite sill (~108 Ma) from coastal SE China, with aims to investigate the possible genetic link between them. The dolerite displays OIB-like trace element features and contains moderately radiogenic Sr-Nd-Pb-Hf and light Ca isotopic compositions. The nearly identical Sr-Pb isotopes between plagioclase and bulk rock indicate a minor role of crustal assimilation during magmatic evolution. The remarkable positive Ba anomalies, similar Sr and Pb isotopic compositions to the contemporary arc-type mafic rocks and light Ca isotopes suggest a source modified by recycled sediments. Additionally, the low La/Nb and Zr/Nb ratios indicate the involvement of an oceanic crust component that experienced dehydration and metamorphism to retain rutile. Further element-isotopic modeling suggests derivation of the parental magma from the asthenospheric mantle source that had been metasomatized by melts from both sediments and mafic oceanic crust. Considering that SE China was mainly influenced by subduction of the Paleo-Pacific Ocean during late Mesozoic, the subducting Paleo-Pacific slab was therefore the most likely candidate for such recycled components. Interaction of the melts from the recycled oceanic slab with the asthenospheric mantle, possibly as a consequence of rollback and tearing of the subducting Paleo-Pacific slab, formed the OIB-type source of the Liucheng dolerite sill.