Receiver function images of the mantle transition zone beneath NE China: New constraints on intraplate volcanism, deep subduction and their potential link

- NECESSArray RF images revealed significant topography of the 660-km.
- The 660-km is highly depressed in a narrow region between ∼40°N and ∼45.5°N.
- Moderate depression of the 660-km is observed in a broad area in latitudes >45.5°N.
- The 660-km is slightly uplifted in a localized area ∼200 km west to Changbaishan.
- Changbaishan is likely caused by a hot mantle upwelling below the slab.

In order to better understand the deep subduction geometry of the Pacific plate and genesis of intraplate volcanism in northeast China (NE China), we computed a total of 45,505 receiver functions from 788 teleseismic events recorded by 255 stations (NECESSArray temporal and permanent stations) in NE China. We used a common-conversion-point stacking (CCP) method to generate a 3D reflectivity volume beneath the study area. To position the P-to-S conversions to the correct depths, we employed 3D crustal and mantle models as references to make time to depth conversion. The 3D reflectivity volume was generated in an area between 115°-135°E and 40°-49°N, in the depth range of 300 to 800 km. We found significant topographic relief on the 660-km discontinuity across the study area. In particular, in a westward Pacific plate subduction section between 40°N and ∼45.5°N, the 660-km discontinuity is depressed by as much as ∼30-40 km along the western extension of the deep seismicity. The depression is elongated along the strike of the deep seismicity and is confined to a 200-300 km region in the E-W direction of subduction. To the west of this depression the 660-km discontinuity is uplifted by 5-10 km in a rectangular area of ∼100 km by 200 km centered at about 125°E and 43°N. In the north, the 660-km discontinuity is moderately depressed (∼20 km) in a broad area that extends further west. The high and low regions in the 660-km topographic map correlate, respectively, with low- and high-velocity anomalies in the P- and S-wave tomographic velocity images at the same depth. Our results suggest that slab stagnation might not be occurring in the southern part of the NE China, where the Changbaishan volcanic complex is located, thus the magmatism is unlikely caused by dehydration of the flat-lying Pacific slab in the transition zone. The low velocity mantle upwelling arising from a gap of stagnant slabs is a likely source that feeds the volcanic complex in NE China.