The role of continental fragments in the formation of intra-oceanic arcs: Constraints from Sr-Nd-Hf-O isotopes of gabbro from the Jiamusi Block, NE China

•Contribution of pelagic and terrigenous sediments to subarc mantle enrichment.•Continental fragments likely occur beneath both fossil and modern intra-oceanic arcs.•Continental fragments facilitate subduction initiation.•Continental fragments also account for continental signature of young island arc magmas.