Seismic images of the mantle transition zone beneath Northeast China and the Sino-Korean craton from P-wave receiver functions

Abstract

Seismic data from northeast (NE) China and the Sino-Korean craton were combined to image the upper mantle discontinuities at 410 and 660km. Fine-scale topographic variations on these two discontinuities provide important clues for both delineating geometry of the subducting Pacific slab particularly at arc–arc junction and interpreting regional Cenozoic intraplate volcanism. We used over 90,000 receiver functions from 1916 teleseismic earthquakes recorded by 584 broadband seismic stations, primary those of temporary seismic arrays. We found the average depths of the two discontinuities to be 410km and 672km, respectively, beneath the study area. Results show that the 660-km discontinuity is strongly depressed by about 20–30km in a narrow region beneath and around the Changbaishan volcano, consistent with the results of previous receiver function studies. In contrast, much of the Sino-Korean craton exhibits typical transition zone thickness (~260km) and thus offers no evidence of a stagnated Pacific slab. Our results also reveal an elevated 660-km discontinuity and a thinner transition zone both to the west of the observed depression region and beneath the Kuril–Japan arc junction. This feature is most likely due to a tearing of the descending Pacific plate at both its leading and junction edges. An additional elevated 660-km discontinuity together with a thinner transition zone appears in the vicinity of the Dariganga lava field, supporting interpretations of a deep-rooted mantle plume. Our observations of an elevated 410-km discontinuity and a thicker transition zone correlate spatially with the diffuse distribution of volcanism around Hannuoba, Aershan and Wudalianchi. This correlation may suggest lithospheric removal as a mechanism for these magmatic activities.