| Qinling orogenic belt is located in the central of china, is the dividing line between Yangtze plate and north china plate, it has a long evolutionary history and a strong degree of deformation-metamorphism, although the results of its great, but there are still many unsolved problems.The paper is based on the Ordos basin before Qinling orogenic belt, and the research ideas of the integration between basin and mountain, relying on tectonic sedimentary evolution process of sedimentary basins in response to episodic events of the adjacent orogenic belts. In the course of the study, the indoor map compilation, outcrop observations, microscopic characterization of rock and zircon dating, geochemical analysis, means and methods are oroganically combined, while focusing on core drilling within the basin data, core analysis, logging data and the integrated use of seismic data. Indoor maps are focused on the compilation of tectonic maps and sedimentary maps with one thousand of drilling well datas and a lot of outcrop datas and few seismic datas. Isotopic datas of zircon are mainly concentrated on the basement and Late Ordovician tuff in the Ordos Basin, the basement research is focused on the basement lithology, metamorphism, zircons and zircon isotopic age and the relationship with the adjacent basements, the research of the Ordovician tuff is focused on the rock assemblages, tuff geochemistry, formation age and tectonic setting reflected. Geochemical datas also include the sedimentary rocks of late Paleozoic and Mesozoic in addition to Ordovician tuff, this outcome gives important insight for the study of Qinling orogenic activity on Late Paleozoic, to a certain extent make up for the blank of Qinling orogenic process on the late Paleozoic. Outcrop observations are focused on the southern margin of Ordos Basin, the tectonic deformation chracteristics emphasize on the organic combination of three-dimensional surface, on the other hand emphasize on the organic combination between the outcrop and the seismic profiles. According to the conclusions of the study, the sedimentary characteristics, structural deformation, magmatic activity characteristics, geochemical characteristics on each period of Ordos basin are able to better respond to the process of the Qinling Orogenic Belt, and then make up some of the blanks for the Qinling orogenic during the study, at the same time may provide a reference for non-mature areas about the response relationship between basin and mountain.The relationship between the formation and evolution of the Ordos Basin and the Qinling orogenic process may be divided into five stages:(1) On the Precambrian, The relationship of the crystalline basement is more closely between the Qinling orogenic and the Ordos Basin than the eastern north china craton and the Ordos Basin. The testing data of zircon show that the distance is far off between the eastern north china craton and the Ordos Basin 2.0 Ga, the sedimentary characteristics and lithologic characteristics and the formation age of the Ordos basin crystalline basement are more closely to Qinling group of the Qinling orogenic belt. (2) On the early Paleozoic, the sourthern Ordos basin has experienced the passive continental margin from Cambrian to early Ordovician and the active continental margin on the middle-late Ordovician with the subduction of Qinling Hai to the Ordos basin. The full trench-arc-basin system is formed between the southern margin of the Ordos basin and Qinling orogenic belt on the evolution stage of the passive continental margin, and where there is the assemblage of the gravity flow and the tuff, and the sedimentary characteristics of the back-arc basin. The geochemical characteristics of tuff reflect island-arc environment, the formation age of tuff is around 450 Ma, and the time is consistent with the granitoid intrusion of island-arc environment in the Qinling orogenic belt. The angular unconformity between Ordovician formation and late Paleozoic formation proves that the existing of Caledonian orogeny movement, the properties of orogeny is the subduction collision and orogeny with Shangdan ocean basin. (3) On late Paleozoic, the northern margin of Qinling orogenic belts are mainly located in the extension satage within the plate, the tectonic activities are relatively stable. The Qinling orogenic belts are not an independent tectonic unit on the stage, but as a part of the southern margin of the Ordos Basin, the background of evolution is the same with the southern margin of the Ordos Basin. The components and geochemistry characteristics of clastic reflect tectonic background on the stage; all samples of Shanxi formation and Shihezi formation are failed into the recycling orogeny on the central and north areas, while some samples are failed into the land mass areas on the southern areas of the Ordos basin, which reflect the relatively stable tectonic features on southern basin. Meanwhile, all samples of Shiqianfeng formation are failed into recycling orogeny on the southern Ordos basin, which reflect the tectonic movement intesity from the Shanxi Formation to Shiqianfeng formation on the southern Ordos basin. (4) On the Mesozoic, the northern margin of the Qinling orogenic belt keep the continuous subduction to the southern margin of Ordos Basin, the strong tectonic deformation are happened, produced a series of magmatic along the edge of the basin. The tectonic deformation is characterized by overall uplift during Indosinian movement and strong thrust structure during the Yanshan movement. The magmatism activities have multi-performance characteristics; most of them are distributed along the deep faults. (5) On the Cenozoic, the Qinling orogenic belts suffer from differential uplift in early, extrusion-translation-wrench movement in late; the results lead to the formation of a series of fault basins, weihe graben is a stable transition zone between the Ordos basin and the Qinling orogenic belts.Innovation of the paper focuses on four areas:(1) The basement age of the Ordos basin were re-tested by zircon dating, although the lack of sedimentary strata, and can not represent the latest age of basement, but two wells 207Pb/206Pb weighted average ages are 2031 ± 10 Ma and 2035 ± 10 Ma, the data is relatively concentrated, more consistent, there is no appearance of Archean age, on behalf of the Paleoproterozoic age. To some extent, the results support the overpoint that west block and east block of north china plate are collided in 1.85 Ga, at least the two blocks are isolated each other in 2.0 Ga. It also supports the overpoint that Qinling Group of Middle Proterozoic has unified ancient crystalline basement with the south of north china plate. (2) The tuff ages are consitent between outcrops section and drilling cores, are concentrated around 450 Ma, the result shows that the tectonic activity of the Qinling orogenic belt is relatively stable during the Early Ordovician, and is the relative activity in the Late Ordovician, the time is beginning of Caledonian orogenic activities of the North Qinling. (3) The sedimentary and geochemistry chracteristics of the clastic rocks show that the activity intensity are different between the northern orogenic belt and the southern orogenic belt of the Ordos Basin during late Paleozoic, the Yinshan orogenic activity is far stronger than Qinling orogenic on early late paleozoic, and with the further evolution of basin, to the late Paleozoic, the activity of Qinling orogenic is strengtheming gradully, both in the horizontal tend to balance, reflecting the activity intensity of the Qinling Mountains between the Caledonian orogenic period and the Indo-China orogenic period. (4) Research of deponding on the deforming characteristics show that the difference of the activity intensity during Indosinian orogenic and Yanshan orogenic, the rapid uplift is performed during the Indosinian movement, the thrust structure is performed during the Yanshan movement. |
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