Tomographic evidence for a mantle transition zone origin of the Wudalianchi and Halaha volcanoes in Northeast China

There exists much debate about the origins of cretaceous-present volcanism in northeast China. Here we present new high-resolution relative P-wave tomographic images of the upper mantle, transition zone and uppermost lower mantle beneath the region. The inclusion of new data from two dense seismic arrays has vastly improved sampling of the upper mantle structure in the region of interest, providing good constraint on the seismic structure under the intraplate Wudalianchi and Halaha volcanoes. A local-scale low-velocity anomaly is revealed in the upper mantle beneath the two volcanoes, whereas large-scale high-velocity anomalies are imaged in the mantle transition zone. These results suggest that the two volcanoes, though located at different sites above the stagnant Pacific slab, are likely associated with the deep subduction and dehydration of the Pacific slab, possibly through the upwelling of wet and hot asthenospheric materials in the big mantle wedge at Wudalianchi and through deeper hydrous upwelling related to slab avalanche at Halaha. Our results also reveal other striking features, such as high-velocity structures resting on the 410 km discontinuity beneath the Great Xing'an Range and the Songliao Basin, which are attributed to the detached continental lithosphere. The delamination most likely occurred in the Cretaceous, which induced widespread magmatism in Northeast China.