P-wave arrival times of both regional and teleseismic earthquakes were inverted to obtain mantle structures of East Asia. No fast （slab） velocity anomalies was not find beneath the 660-kin discontinuity through tomo...P-wave arrival times of both regional and teleseismic earthquakes were inverted to obtain mantle structures of East Asia. No fast （slab） velocity anomalies was not find beneath the 660-kin discontinuity through tomography besides a stagnant slab within the transition zone. Slow P-wave velocity anomalies are present at depths of 100-250 km below the active volcanic arc and East Asia. The western end of the flat stagnant slab is about 1 500 km west to active trench and may also be correlated with prominent surface topographic break in eastern China. We suggested that active mantle convection might be operating within this horizontally expanded ＂mantle wedge＂ above both the active subducting slabs and the stag- nant flat slabs beneath much of the North China plain. Both the widespread Cenozoic volcanism and associated extensional basins in East Asia could be the manifestation of this vigorous upper mantle convection. Cold or thermal alaomalies associated with the stagnant slabs above the 660-km discontinuity have not only caused a broad depression of the boundary due to its negative Clapeyron slope but also effectively shielded the asthenosphere and continental lithosphere above from any possible influence of mantle plumes in the lower mantle.展开更多
We measured Fe isotopic compositions of mineral separates of harzburgite, dunite and chromitite from Luobusa, Tibet as well as two harzburgites from Zedang for comparison to constrain the origin of podiform chromite d...We measured Fe isotopic compositions of mineral separates of harzburgite, dunite and chromitite from Luobusa, Tibet as well as two harzburgites from Zedang for comparison to constrain the origin of podiform chromite deposits.展开更多
基金grants(B-11440134,S-12002006)to Dapeng Zhao from the Japan Society for the Promotion of ScienceSupport for Shunping Pei came from a postdoct grant of Peking University+1 种基金supported by the National Natural Science Foundation of China(Nos.40125011,90814002 and 41074041)the Chinese Academy of Sciences(No.KZCX2-EW-QN102)
文摘P-wave arrival times of both regional and teleseismic earthquakes were inverted to obtain mantle structures of East Asia. No fast （slab） velocity anomalies was not find beneath the 660-kin discontinuity through tomography besides a stagnant slab within the transition zone. Slow P-wave velocity anomalies are present at depths of 100-250 km below the active volcanic arc and East Asia. The western end of the flat stagnant slab is about 1 500 km west to active trench and may also be correlated with prominent surface topographic break in eastern China. We suggested that active mantle convection might be operating within this horizontally expanded ＂mantle wedge＂ above both the active subducting slabs and the stag- nant flat slabs beneath much of the North China plain. Both the widespread Cenozoic volcanism and associated extensional basins in East Asia could be the manifestation of this vigorous upper mantle convection. Cold or thermal alaomalies associated with the stagnant slabs above the 660-km discontinuity have not only caused a broad depression of the boundary due to its negative Clapeyron slope but also effectively shielded the asthenosphere and continental lithosphere above from any possible influence of mantle plumes in the lower mantle.
文摘We measured Fe isotopic compositions of mineral separates of harzburgite, dunite and chromitite from Luobusa, Tibet as well as two harzburgites from Zedang for comparison to constrain the origin of podiform chromite deposits.
