Host: Abstracts of Annual Meeting of the Geochemical Society of Japan
Name : Abstracts of Annual Meeting of the Geochemical Society of Japan
Number : 72
Date : September 07, 2025 - September 19, 2025
Pages 190-
Detailed 3-D images of whole-mantle P-wave velocity (Vp) structure beneath West Pacific and East Asia are obtained by using an updated method of multiscale global tomography. The 3-D Vp structure from the crust to the core-mantle boundary (CMB) is effectively resolved. Our tomography confirms well-known features revealed by previous studies, such as high-Vp zones corresponding to the subducting Pacific and Philippine Sea slabs, as well as low-Vp zones in the crust and upper mantle beneath active arc volcanoes. The subducted Pacific slab becomes flat in the lower part of the mantle transition zone (MTZ) beneath East Asia, and a big mantle wedge (BMW) has formed above the flat slab. Active intraplate volcanoes (e.g., Jeju, Changbai and Wudalianchi, etc.) are underlain by low-Vp anomalies in the BMW, suggesting that the intraplate volcanism is caused by hot and wet upwelling flow in the BMW. The great Tanlu fault zone is a boundary between western and eastern parts of the BMW, which exhibit different features of velocity structure and seismic anisotropy. Beneath the Izu-Bonin trench, high-Vp zones appear from the MTZ to CMB, suggesting that the Pacific slab subducts all the way down to the CMB. In contrast, a continuous, thin low-Vp zone is revealed from the surface to the CMB beneath the Hainan hotspot, reflecting the Hainan plume that exists in the whole mantle. Under SE Asia, subducted slabs, mantle plumes and BMW are also imaged clearly. Beneath the Australian slab that has subducted into the lower mantle, a strong low-Vp anomaly is detected, which may reflect subslab hot mantle upwelling (SHMU) due to return flow of the slab deep subduction. In particular, windows (holes) in the subducting Australian slab are revealed beneath North Sumatra and eastern Java. The low-Vp anomaly in the mantle wedge above the Australian slab is connected with the SHMU through the slab windows, suggesting that mixture of the island arc magma and the SHMU may have caused super-eruptions of the Tambora and Rinjani volcanoes in eastern Java and the Toba volcano in North Sumatra.
