Late Paleozoic–Mesozoic subduction and accretion of the Paleo-Pacific Plate: Insights from ophiolitic rocks in the Wandashan accretionary complex, NE China

The Wandashan accretionary complex (AC), consisting of the Raohe and Yuejinshan complexes, is located on the continental margin of Northeast Asia and represents an excellent source of information about Paleo-Pacific subduction and accretion. However, the protolith nature and tectonic evolution of the Wandashan AC are under debate. This contribution reports new geochronological, geochemical, and Sr-Nd-Pb-Hf isotopic data for ophiolitic rocks from the Wandashan AC. The 169–166 Ma plagioclasites and homogeneous gabbros from the Raohe complex are OIBs while 228–214 Ma homogeneous gabbros are continental VABs. Cumulate gabbros from the Yuejinshan complex formed at 280–278 Ma and ~220 Ma and have similar characteristics with E-MORB and N-MORB, respectively. They are BABBs and their primary magma was derived from a source region between EMI and EMII that was affected by continental crustal contamination as well as subduction-zone metasomatism. Combined with previous studies, we suggest that the onset of subduction of the Paleo-Pacific Plate was in the Early Permian. Subsequently, a back-arc basin, whose present suture is on the eastern margin of the Jiamusi Massif, formed and widened during 280–232 Ma, after which the basin closed and BABBs were emplaced to form the Yuejinshan complex during 210–180 Ma. The formation of VABs of the Raohe complex is coincident with the closure of the back-arc basin, and together with the 169–166 Ma OIBs, they constitute a major part of the Raohe complex. The accretionary process was completed during 133–131 Ma. Taken together, the ophiolitic rocks indicating multistage magmatism in the Paleo-Wandashan region recorded the formation-closure process of back-arc basin and the accretionary process of the Wandashan AC, during the westward subduction of the Paleo-Pacific plate. The back-arc basin identified in our study sheds new lights on geodynamic evolution model of subduction and accretion of the Paleo-Pacific Plate on the continental margin of NE Asia.