| The rheology of the lithosphere is the key to understanding the deformation mechanism and tectonic evolution of the Tibetan Plateau.Although different geodynamic models such as rigid block extrusion,continuous deformation,and mid-lower crustal flow have been proposed the deformation mechanism of the Tibetan Plateau,the interactions between the Tibetan Plateau and its surrounding blocks are still under debate.Compared with seismic velocity,seismic attenuation has a very different dependence on temperature,partial melting,and volatile content,which can provide new insights into the rheology of the lithosphere.Based on the 20-143 s Rayleigh wave data recorded at 350 ChinArray temporary stations in the southeastern Tibetan Plateau,we employed the two-plane-wave method to invert for the shear wave velocity and attenuation structures of the crust and upper mantle.In order to compare the lithospheric structures of different blocks,we divided the research area(97°E108°E,21°N-30°N)into four subregions.Finally,we obtained the shear wave velocity structure of the crust and upper mantle of the southeastern Tibetan Plateau and the shear wave attenuation structure of the crust and upper mantle of the part of southeastern Tibetan Plateau.The results show that(1)the low velocity and strong attenuation layer beneath the Songpan-Ganzi block indicates a stratified rheological structure in this region,which has a relatively soft mid-lower crust and strong lower crust.The existence of seismic anomalies in the mid-lower crust may be due to the elevated temperature,which is caused by the crustal thickening.(2)The top of upper mantle of Yangtze block and Indo-China block show obvious low velocity features and the strong attenuation further suggests these anomalies are related to the presence of partial melting.The mantle upwelling,which is resulted from the lithosphere detachment,provides the heat sources for the partial melting. |
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