HR: 1330h
AN: T32B-0934    [PDF]
TI: Origin of the intraplate volcanism and the fate of the subducting Pacific slab under Northeast Asia
AU: * Zhao, D
EM: zhao@sci.ehime-u.ac.jp
AF: Ehime University, Geodynamics Research Center, Matsuyama, 790-8577 Japan
AU: Lei, J
EM: leijs@sci.ehime-u.ac.jp
AF: Ehime University, Geodynamics Research Center, Matsuyama, 790-8577 Japan
AB: Recent global tomographic results show that the subducting Pacific slab becomes stagnant in the mantle transition zone under Northeast (NE) Asia. Receiver function analyses revealed that the 670 km discontinuity under NE China shows a complicated multi-discontinuity feature caused by the interaction between the subducting slab and the mantle transition zone. In addition, two active intraplate volcanoes, Changbai and Wudalianchi, exist in NE China. It is unclear whether these intraplate volcanoes are hotspot or not. To clarify the fate of the subducting slab and the origin of the intraplate volcanism, we determined a high-resolution 3-D whole-mantle structure under the region using the ISC data set as well as arrival times recorded by 24 portable and permanent seismic stations installed recently in NE China. A large number of arrival times of P, pP, PcP, PP are picked from over 100 teleseismic events (epicentral distances 25 to 100 degrees). Our results show that the subducting Pacific slab is clearly imaged under the Japan Islands and the Japan Sea, and deep earthquakes occurred within the slab. The slab-related fast anomalies extend toward the west, which are clearly visible in the transition zone under NE Asia. Pieces of fast anomalies are visible in the lower mantle down to the CMB. These results suggest that the subducting Pacific slab becomes stagnant in the transition zone under NE Asia before finally collapsing down to the lower mantle as a result of very large gravitational instability from mantle phase transitions. Very slow anomalies exist in the upper mantle right beneath the Wudalianchi and Changbai volcanoes, right above the stagnant Pacific slab in the transition zone. These results suggest that the active volcanoes in NE China are not hotspot but a sort of back-arc volcanoes which are closely related to the subduction process of the Pacific slab. Slow velocity anomalies in the back-arc region are generally associated with the back-arc magmatism and volcanism caused by the deep dehydration process of the subducting slab and the convective circulation process of the mantle wedge. These processes lead to the large-scale upwelling of the asthenospheric materials under NE Asia and cause intra-plate volcanism and continental rift systems in the region.
UR: http://www.ehime-u.ac.jp/~grc/
DE: 1212 Earth's interior--composition and state (8105)
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 7207 Core and mantle
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8124 Earth's interior--composition and state (old 8105)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting