| South Dabashan Mountain tectonic belt is seated at the north margin of the Upper Yangtze block, the connection area of Sichuan basin and south Qinling orogenic belt, which lies adjacent to the Micangshan Mountain in west and to the high and steep orogenic belt in east and takes on a southwest-protruded arc orogenic belt in the whole at a macro view. The belt is the compound production of thrust movement of two periods both in Indosinian stage and Yanshanian stage. Thus two stages' movements forged the distinctive arc orogenic system of present South Dabashan Mountain, together with the special foreland basin(intra-continental foreland basin). After synthesized study of modern tectonics methods, geophysics and isotopic chronology and so on, following the thought of "section-divide in strike, belt-divide in inclination and layer-divide in vertical direction", the present tectonic of South Dabashan Mountain Zhenba-Chengkou section is analyzed in detail. What's more, with the help of Zircon chronology data in tracing the provenance area of Dabashan Mountain foreland basin, its tectonic evolution and mountain-basin coupling relativities are discussed in particular. From these studies, some advances are acquired as follows:1. After comparing the Permian strata of northern margin of Yangtze and Gaochuan basin in special, we discover that the Permian deposit is predominated by carbonate rocks of platform facies in northern margin of Yangtze(especially the Zhenba area) while black rock series of Guojiaya Formation of Permian distributes in Gaochuan basin. Considering the regional tectonic, Guojiaya Formation is the residual of the rift-limited oceanic basin between Yangtze block and Qinling micro-plate, and is formed under the background of regional extensional environment, which is consistent with the Permian basalt eruption event of Emei mountain resulted by regional extensional environment.2. The paper is based on detail route survey towards geological structures on the ground surface of the study area and large scale mapping for key area, and basically makes clear the present tectonic characteristics of South Dabashan Mountain Zhenba-Chengkou section. According to tectonic patterns and deformation assemblages, the principle of section-divide in strike, belt-divide in inclination and layer-divide in vertical direction are put in the study of South Dabashan Mountain, which is divided into east, middle and west in strike, imbricate thrust belt, fault fold belt and thrust stretched deformed belt in inclination and upper, middle and lower in vertical direction through regional decollement and geophysics data. From the root of South Dabashan Mountain to the foreland basin, the deformation becomes weaker and weaker, the shape of fold gets wider and wider and the strata of outcrop turns newer and newer. Meanwhile, the decollemen lifts to plaster salt rocks of Triassic from north to south. And the structures shape on the ground surface is mainly the box-shaped folds, tightly closed folds, fan-shaped folds and Jurassic folds.3.We believe that two periods' folds developed at the connection between eastern Micangshan Mountain and western Dabashan Mountain and identify that nearly east-west-northeast by east orientated fold formed earlier than the fold of nearly south-north-northwest by west orientated through superimposed study of large scale mapping towards Sishang area of Xixiang county. Combined with regional unconformity event and chronology data of predecessors, it can be concluded that both two periods' folds formed in J3-K1 and the nearly east-west orientated fold formed earlier that that of south-north orientated.4.Through Zircon chronology study of clastic rocks of Xujiahe Formation of Triassic and upper Shaximiao Formation of Jurassic in intra-continental foreland basin of Dabashan Mountain, we find that the clastic Zircon age is similar to that of Qinling-Daba area. Considering regional data, we put forward that the detrital deposits of Dabashan foreland basin is mainly derived from the productions of intra-continental orogenic magmatism in middle-late period of Mesozoic of Qinling orogenic belt(213Ma～283Ma; 163Ma～274Ma), northern Qinling(312Ma～448Ma; 404Ma), southern Qinling(694Ma～710Ma; 712Ma),Qinling(1430Ma～1988 Ma; 1742Ma～1972Ma), the basement of Qinling orogenic belt(2133Ma～2708Ma; 2116Ma～2594Ma,3025Ma～3140Ma). Study shows that the foreland basin keeps communication with Qinling-Daba orogenic belt in material and the two tectonic units exist mutual coupling relativities in material composition.5.Recovering the tectonic events sequence of South Dabashan mountain since Mesozoic-Cenozoic:①Suffering the early effect between the South China block and the North china block, South Dabashan area was deformed and which resulted in Xujiahe Formation of Triassic angular unconformity overlaid on the lower Triassic in Chengkou and Pingba area. At that time, Chengkou-Pingba fault may be formed and active, but the major area of South Dabashan were not folded and deformed;②The large-scale intra-continental subduction of the Southern Qinling in Yanshanian resulted in the thrust of Middle-Lower Jurassic strata in Wafangdian of North Dabashan area, and involved in the South Dabashan again, which caused the fold and deformation in the area . And folds and thrust faults formed in line, yet dextral strike-slipping may superposed at the same time;③Since Cretaceous Period, the study area has been uplifted and denuded in the whole with the impact of Himalaya movement and comes to today's visage finally.
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