| China continent turn into intracontinental tectonic evolution process after the continental collage in the indosinian, and tectonic differentiation and differences evolution occurred in the east and west parts during the Mesozoic to Cenozoic. As the axial transformation zone of this differences evolution and deep dynamic process, the Helan-Sichuan-Yunnan- N-S tectonic belt (HLSYNSTB) show the unique characteristic of the continental tectonic deformation and the process of deep adjustive transformation, and record the well deformation trace of continental tectonic and intracontinental tectonic, and imply more information about the continental dynamics. The Longmenshan tectonic belt (LMSTB) and the Sichuan-Yunnan tectonic belt (SYTB) which forms the middle-south parts of the HLSYNSTB turn to the eastern boundary of the material eastward motion of the Tibet Plateau with the uplift in the Cenozoic after the evolution and development of Tethys tectonic domain in the Mesozoic. And as the result of the development and evolution in the Meso-Cenozoic, the Longmenshan and SYTB form nowdays composite superimposed tectonic system of HLSYNSTB and eastern boundary of Tibetan Plateau. So the Longmenshan and SYTB are the ideal areas to know the formation and evolution of the HLSYNSTB and the eastern boundary of Tibetan Plateau, and are the key areas to explore the scientific problem of the continental tectonic, such as stages, orientation and strain field of China intracontinental tectonic deformation. Further they are the natural laboratorys to study the continental tectonic and intracontinental tectonic deformation.Based on the existing geological data, detailed field observation and experiment results, this paper mainly chooses the southern part of LMSTB and the northern part of SYTB as the target region, and applies multidisciplinary combination means as research means and then carries out the research of structural analysis, rock fabric and chronology. It finds out the existing basic geological fact and determines the tectonic deformation sequence of the southern section of LMSTB and the northern part of SYTB. Furthermore, it also deeply analyzes their transition relations, evolution process and mechanism. The main results achieved and understanding are as follows:(1) LMSTB and SYTB in nowadays is a complex tectonic system composited and superposed by multi stages of tectonic deformation since Indosinian. This paper determined three stages of tectonic deformation. The frist stage, under the background of Paleo-Tethys ocean basin closing and collision orogeny in Late Indosinian, the LMSTB and Jinpingshan tectonic belt which was in SYTB occurred intercontinental orogenic tectonic deformation on the basis of the original Panxi rift on the western Yangtze Block. And that produced a large-scale thrust-nappe structure from west to east to the northwest to southeast and left-slip ductile shear extrusion deformation developed in boundary main faults. Eventually, they forming a unified long-term and nearly north-south trending Longmenshan-Jinpingshan thrust fold tectonic belt which forming and establishing the prototype and tectonic evolution foundation for the middle south section of HLSYNSTB. The second stage, by the far field effect of Neo-Tethys tectonic evolution in Late Mesozoic (J3-K1), the Longmenshan-Jinpingshan tectonic belt continue to developed thrust nappe deformation on the basis of the thrust fold tectonic belt which formed in the first stage, and developed the isoclinal folds, dense cleavage, thrust faults, then superposed and transformed early intercontinental orogenic structure. Meanwhile, tectonic deformation expanded and evolved eastward, and began to develop and form the NW trending fault-fold belt in Daliangshan region. Eventually Longmenshan-Jinpingshan fold-thrust belt formed as the main part of middle south section of HLSYNSTB and laid the tectonic framework of north-south tectonic belt in Mesozoic. The third stage, it is occurred in Cenozoic. Under the background of collision orogeny of Indian plate and Eurasian plate, sharp uplift of the Tibetan Plateau, eastward movement of the material, newborn Xianshuihe fault belt cut off the Longmenshan-Jinpingshan fold-thrust belt, and NW to SE thrust nappe structure was developed in Longmenshan fault belt in the northside, while north-south trending Xianshuihe-Anninghe-Daliangshan-Xiaojiang fault left-shearing strike-slip structure was developed in the southside. The structure of this stage superposed and destroyed the HLSYNSTB which was mainly dominated by Longmen-Jinpingshan fold-thrust belt in Mesozoic, and eventually formed current composite and superimposed structure system of HLSYNSTB and eastern edge of the Tibetan Plateau.(2) In Cenozoic, under the background of regional tectonic and dynamic of collision orogeny between Indian plate and Eurasian plate and different northward movement of Indian Plate and Australian plate, the eastern section of Tibetan Plateau was blocked by Yangtze Block of the South China Plate, and caused it started to rotate clockwise taking Eastern Himalayan Tectonic Syntaxis as the center, and some part also began to escape and deflect southeastward and gradually expand outwards. And then Xianshuihe faoult belt was developed at its most peripheral section, and the migmatite (47-27Ma) and Zheduoshan syntectonic granite (18-12Ma) were formed and emplacement. With the further development of rotating, Xianshuihe fault belt expanded southward along the weak belt of crust of Anninghe, Daliangshan, Xiaojiang fault and so on, forming the Xianshuihe-Anninghe-Xiaojiang strike-slip fault system (5.5Ma) in the eastern boundary of the Tibetan Plateau, and showing general characteristics of clockwise rotation taking Eastern Himalayan Syntaxis as the axis and southeastward and southward escape of the substance in Sanjiang tectonic belt and Chuandian block between Eastern Himalayan Syntaxis and Xianshuihe-Anninghe-Xiaojiang fault belt.(3) Nowadays, the "Y" shape tectonic framework formed by LMSTB and SYTB is the result of composition and superposition of Mesozoic Tethyan tectonic and the tectonic of eastern boundary of Tibetan Plateau in Cenozoic. Long-term near north-south trending Longmenshan-Jinpingshan fold-thrust belt which was developed under the affect of intercontinental tectonic deformation in Late Indosinian and late Mesozoic was cut off by Cenozoic Xianshuihe fault belt protruding to the NE, forming Jinpingshan tectonic belt at the north side and the LMSTB at the south side. The former shows as NE trending structure nowadays, since Songpan-Garze block eastward moved and was blocked by Yangtze block while substance extruded eastward and north-eastward. The latter together with the south extended segment of the NW trending Xianshuihe fault belt, Anninghe, Daliangshan and Xiaojiang N-S tectonic belt constitute SYTB. N-S trending SYTB, NE trending LMSTB and NW trending Xianshuihe fault belt together constitute the visible "Y" shape tectonic framework at the current edge of eastern margin of Tibetan Plateau. |
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