The thickness and structural characteristics of the crust across Tibetan plateau from active-sources seismic profiles
Qiusheng Li 1,2,Rui Gao 1,2 Zhanwu Lu 1,2 Ye Guan 1,2 Jisheng Zhang 1,2 Pengwu Li 1,2 Haiyan Wang 1,2 Rizheng He 1,2 and Marianne Karplus3 1 Lithosphere Research Center,Institute of Geology,Chinese Academy of Geology Science,Beijing 100037,China 2 Earthprobe and Geodynamics Open Laboratory of Chinese Academy of Geology Science,Beijing 100037,China 3 Crustal Geophysics Group,Stanford University,Stanford CA 94305,USA
The Tibetan plateau as one of the youngest orogen on the Earth was considered as the result of continent-continent collision between the Eurasian and Indian plates.The thickness and structure of the crust beneath Tibetan plateau is essential to understand deformation behavior of the plateau.Active-source seismic profiling is most available geo-physical method for imaging the structure of the continental crust.The results from more than 25 active-sources seismic profiles carried out in the past twenty years were reviewed in this article.A preliminary cross crustal pattern of the Tibetan Pla-teau was presented and discussed.The Moho discontinuity buries at the range of 60-80 km on average and have steep ramps located roughly beneath the sutures that are compatible with the successive stacking/accretion of the former Cenozoic blocks northeastward.The deepest Moho(near 80 km) appears closely near IYS and the crustal scale thrust system beneath southern margin of Tibetan plateau suggests strong dependence on collision and non-distributed deformation there.However,the ～20 km order of Moho offsets hardly reappears in the inline section across northern Tibetan plateau.Without a universally accepted,convincing dynamic explanation model accommodated the all of the facts seen in controlled seismic sections,but vertical thickening and northeastern shorten of the crust is quite evident and interpretable to a certain extent as the result of continent-continent collision.Simultaneously,weak geophysical signature of the BNS suggests that convergence has been accommodated perhaps partially through pure-shear thickening accompanied by removal of lower crustal material by lateral escape.Recent years the result of Moho with ～7 km offset and long extend in south-dip angle beneath the east Kunlun oro-gen and a grand thrust fault at the northern margin of Qilian orogen has attract more attention to action from the northern blocks.The broad lower-velocity area in the upper-middle crust of the Lhasa block was once considered as resulted from partially melted rocks.However the low normal vP/vS ratio and the Moho stepwise rise fail to support significant partial melting in the middle-lower crust of the central-northern Tibetan plateau.Furthermore,the lower-velocity of crust occasionally disappears,and/or local thinned exhibits their non-stationary spatial distribution.
【Fund】： financed by the Ministry of Land and Resources of China (2004DKA20280-2-5);; International Sciences and Technology cooperation (2006DFA21340);; the special funds for Sciences and technology research of public welfare trades (200811021);; the key innovation project for sciences and technology of Ministry of Land and Resources (1212010711813);; the China Geology survey Bureau and resources land investigation project(1212010611809);; the Basic outlay of scientific research work from Ministry of Science and Technology of the People's Republic of China (J0803);; the National Natural Science Foundation of China (40830316 and 40874045);; SINOPPROBE-Ⅱ and Open Fund (NO.GDL0603_) of Key Laboratory of Geo-detection (China University of Geosciences Beijing) Ministry of Education”
【CateGory Index】： P315.33
【CateGory Index】： P315.33