Origin And Its Tectonic Significance Of The Late Triassic Extension In The Helan Mountain Area

The provenance and the time-space evolution of Late Triassic in Helan mountain area is to restore the northern section of the western Ordos basin primary basin boundary. The analysis of the time-space distribution characteristics of the basin sedimentary strata and the sedimentary facies evolution rule is an important link. It is an important premise and basis for the objective evaluation of the distribution characteristics of oil and gas resources in reformed basin and scientific prediction of favorable exploration zone.Helan mountain area lies in the joint of the multiple tectonic units, experienced a complicated sedimentary tectonic evolution history. Those who study the late Triassic provenance attribute in Helan mountain area must consider the influence of these factors. Through the evolution process of tectonic units surrounding the Helan mountain system analysis, the emphasis of the thesis, considering the influence of the paleo Asian Ocean collision closing process and Mianlue Ocean collision closing process in late Triassic sedimentary evolution in Helan mountain area. And at that time the Helan mountain area are mainly under the background of passive extensional rift environment. In addition, the main consideration of post transformation characteristics of formation process of the study area of late Jurassic and the Cenozoic in Yinchuan graben and Hetao basin. Combined with the regional tectonic background and post transformation degree, based on the balanced section method, combined with the study area main fault slip recovery and the relative position of small block recovery, the sedimentary range scope of the late Triassic in Helan mountain area is reasonably deduced.The research mainly uses ancient flow testing, gravel composition, geochemistry, thin section identification, cathodoluminescence and heavy mineral combination method. Those who think the Helan mountain late Triassic provenance is multi-source, mixed source, and upper and lower sections of temporal differential evolution characteristics. Provenance of the late Triassic mainly in the northwest, east and west, and occurs in Rujigou and Xiangbangzigou area mixed provenance. The northwest provenance is mainly of Precambrian metamorphic rocks, Paleozoic magmatic rocks and sedimentary strata above the Alashan massif, the southern section of the western region is mainly of basic volcanic rock above the Alashan massif, the eastern region is mainly of the Paleozoic sedimentary strata. Based on five small interval of Yangchang formation, comparing the characteristics of provenance that have certain differences in provenance direction during different periods. Provenance of the T3y1、T3y2、T3y3 mainly in the northwest and southwest. At this moment Helan mountain basin and Ordos basin is connected with a wide range. T3y4、T3y5 began to appear east of the provenance clearly in Huangcaotan and its east. At that time Helan mountain basin and Ordos basin is still connected. Because the eastern area of the entrance of Rujigou has uplift, the scope of the connected began to shrink. The direction of some provenance in Rujigou and Xiangbangzigou mixed source along the Dashuigou area flow into the Ordos Basin. Combined with regional tectonic environment and the tectonic characteristics of the adjacent regions, points out that the provenance properties of Yanchang formation of the late Triassic in the Helan mountain area were significantly different from the different parts of the study area, and the provenance of space and time evolution of the model is attempted to be established.