The Crustal Shortening And Reconstruction Of The Main Terranes Though Mesozoic-Cenozoic In Qinghai-Tibet Plateau

Qinghai-Tibet Plateau, as the product of India-Eurasia collision, is the most complex and special tectonic belt in the world, because of the terranes disperse, convergence and collision periodically during Mesozoic-Cenozoic. It is one of hot issues in Tibetan research to study the mode, process and kinetics of the crustal shortening during Mesozoic-Cenozoic. Different scholars have done much qualitative and quantitative research about the crustal shortening and shortening value of the Qinghai-Tibet Plateau with different methods. In this paper, based on the systematic collection, analysis and research of the existing data and results of Himalayas, Lhasa and Qiangtang terranes, we made the balanced cross-section study in Qiangtang terrane which have scarce research results, the Lhasa terrane that research data vary greatly, and the Langjiexue terrane divided from Tethyan Himalaya. The line-balanced cross-section of the interface between mid-Jurassic Xiali fomation (J2x) and upper Jurassic Suowa formation (J3s) shows that the Jurassic strata shortened by 25.18% in north Qiangtang terrane, the result of the interface between under segment of late Jurassic Suowa formation (J3s1) and upper segment (J3s2) is 33.57% in south Qiangtang terrane. The crustal shortening of Jurassic strata in south Qiangtang is larger than that of north Qiangtang, this may be related to the closure of Bangong-Nujiang suture and the northward underthrust of Lhasa terrane. The balanced cross-section in Lhasa terrane is divided to two sections by central volcanic rocks, for the southern section, viz. the southern fold belt of Cuoqin basin, the Late Cretaceous strata of Jingzhushan fomation is shortened by 20.68%; for the northern section, from south margin of Bangong-Nujiang suture to central fold belt of Cuoqin basin, the shortening value of the interface between Zenong group (K1z) and Duoni formation (K1d) of Early Cretaceous is 25.3%, our results are much smaller than the existing data of the terrane boundary and internal thrust fault systems, it is proved that the Cenozoic crustal shortening was absorbed mainly by the fold and thrust fault systems. The Langjiexue terrane, located in eastern Tethyan Himalaya, the crustal shortening of Triassic Jiangxiong Group is up to 75%, higher than previous studies of the Tethyan Himalaya, 56%-60%. After contrasting our research results and the existing data, we analyzed the shortening process and tectonic deformation about the three terranes, and consider that the shortening process is not a uniform process in each terrane, the intraterrane deformation was mainly absorbed by the boundary of the stable block, suture zone and large thrust systems. The Cenozoic internal deformation in Qiangtang and Lhasa terranes is less than Himalaya. Then, Considering that the results come from different methods vary considerably, in order to have an uniform standards for tectonic reconstruction, we chose the data of balanced cross-section as the basis for terranes reconstruction, and contrast the results from conjugate shear angle analysis and the rock stress analysis, use the MapGIS software to reconstruct the Qiangtang, Lhasa, the Tethyan Himalaya terranes shape including Langjiexue terrane in different periods, which used widely in Geology, our study results will provide the basis for palaeogeographic and paleo-tectonic reconstruction of the Qinghai-Tibet Plateau.