[S14-1] Upper mantle and transition zone dynamics and structure I

[S14-1-03] Slow velocities and thin transition zone indicate upwelling lower mantle beneath eastern Eurasia

^○Christine Houser¹, Alex Webb² (1.Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan, 2.Department of Earth Sciences, Hong Kong University, Hong Kong, China)

When comparing shear velocity and transition zone thickness, eastern Eurasia and the central Pacific stand out with distinctive and robust signals of slow velocities and a thin transition zone. The central Pacific lies on top of a column of slow material rising off of the Pacific large low shear velocity province. Thus, it seems the region experiences upward return flow from the lower mantle. The combination of slow velocities and a thin transition zone indicate the area is warm or dry or both. However, eastern Eurasia is a convergence zone with a long history of subducting oceanic slabs. In addition, independent compressional velocity models find the same low velocity structure within the transition zone on top of faster velocities below in the lower mantle. The tectonic history of the region indicates that the Pacific slab has been rolling to the east since the beginning of Cenozoic. We suggest that the seismic signals in the transition zone are due to upwelling lower mantle material caused by the Pacific slab sweeping across the transition zone as it falls into the lower mantle.