Tectonic Framework Of Phanerozoiceon And Distribution Law Of Regional Mineral Resources In Helanshan Mountain, Ningxia Province,China

Helan Mountain is located at the nodal region of geotectonic element of East and West China, where is the tectonic, geomorphic and also geophysical boundary in North China and also one of the region that thrusting nappes is well developed. Even attention has been paid to it for its special characteristics of geological structure and tectonism, the viewpoints about the Helan rift, thrusting nappe structure, orogenic belt of Qilian Mountains and the boundary of Helan-Mountains rift, have not reached to a consistent understanding, especially lacking the Phanerozoic structural characteristics of Helan Mountains. Supported by the project of "1:250000 regional geological survey of Yinchuan map and Jilantai map ", we obtained more understanding from field and also fundamental data to focus on the tectonic framework and evolution of Helan mountain in phanerozoic period.Here based on new dataset from aspects of field structure characteristics, rock formations and geochemical data, new light has been reached on thrust nappe structure in Helan Moutains, Helan rift effect in Early Palaeozoic, tectonic framework and evolution of Helan Moutains, the boundary of Qilian Orogenic Belt and Helan cold rift.Our geological survey showed that Helan moutain belongs to the intra-plate orogenic belt, which is obviously different from that of marginal or intercontinental orogen. Its main body remains the crustal structure of North China plate, showing remarkable Smith stratigraphic characteristics, especially in the north part of the boundary between Qilian Orogenic Belt and North China plate. This is different from the typical intra-plate orogenic belt with strong tectonic deformation and magmatic activity.Our geological survey further proved that the thrusting nappe structures are relatively well developed in Helan Mountains, reflecting multiple phases of the tectonic evolution and deformation of the Caledonian, Indo-Chinese, Yanshanian and Himalayan periods during Phanerozoic era. The dynamic mechanism is related to the remote effect of collision tectonics between Mid-Qilian - Qaidam continental block with North China block, and between Tethys Sea and Indian plate with Eurasian plate. Here our results contribute to the remote effect.The Rujigou detachment fold is the typical Jura-type structure; and its floor fault has one or two layers structure, which is typical structure of detachment fault in Helan-Mountains tectonic belt. The Mi-zi Type tectonics in the south-middle part of the studied area experiences double effects from thrusting nappe systems of Helanshan Mountains-Lioupanshan Mountains, and superposition of multi-stage tectonic evolutions from Caledonian period to Himalayan period. That is, the Mi-zi Type tectonics, is the superposition of linear fractures in different evolution stages.Our study confirmed the existence of Helan Mountain rift, the record of sedimentary formation is Miboshan Group, and its tectonic pattern can be regarded as the passive mode of cold rift, and its timing can be stricted from Guniutan period of Early Ordovician to Miaopo period of Middle Ordovician.According to the analysis of continental shelf, continental slope transfer zone, foreland basin and boundary faults, and also with respects to th geophysical data, it is suggested that Tujingzi-Qingtongxia Fault could be regarded as the boundary belt of Qilian Orogenic Belt and North China block, the Upper Devonian series on the south side of Weigoujing Fault marks the northeast boundary of Qilian fold system.Based on the characteristics of sedimentary formation and tectonic deformation, the regional tectonic evolution of Helan Mountains in Phanerozoic can be divided into five stages: intra-plate cold rift-continental margin basin, uplifting and planation, depression of continental basin-epicontinental sea, intraplate deformation (extension-compression) and basin-range structure. In this thesis the tectonic framework, deformation features and corresponding tectonic-magmatic event of each evolution stage has also been studied. Especially, progress are made in new understanding on the stages of intraplate deformation (J-K) ,basin-range structure (E-Q) and cold rift. Meanwhile, the analysis and summary of distribution of mineral resources in the studied area by the control of tectonic framework of Phanerozoiceon and sedimentary formation are also presented in this thesis.