CRUSTAL STRUCTURE OF SE TIBET FROM RECEIVER FUNCTION METHOD

As the front region of plate collision, the southern Tibet has always been the hotspot in geoscience research. To reveal the features of the crustal structure of collision frontal zone, we used 2487 tele-seismic records recorded by 38 broadband stations in the southeastern Tibet. Then we calculated the crustal thickness and Poisson’s ratio of this area by CCP stacking and H-κ stacking. The results of the crustal thickness obtained by the two methods are in good agreement, and the crustal thickness in the southeastern Tibet has obvious difference in east-west and north-south. The depth of Moho varies greatly in the Himalaya tectonic zone, ranging from 65 to 80 km. The depth of Moho in Lhasa block ranges from 72 km to 80 km. The crustal thickness on both sides of the Yarlung Zangbo suture has been abruptly changed. The difference in thickness between the north side and the south side of the suture is about 8 km. The average Poisson ratio in the study area is 0.24, which is consistent with the feather that the Poisson ratio in most orogenic belts is low. A strong transition interface exists widely in the middle and lower crust of the study area, the interface may be the upper interface of the high-velocity layer in the middle-lower crust, with a depth of 40~70 km. It is indicated that deep melting or partial melting occurred in the crust, leading to gravitational differentiation and forming a high-velocity thin layer in the middle-lower crust.

Key words: southeastern Tibet; receiver function; H-κ stacking; CCP stacking; crustal structure