Study On The Classification,Characteristics And Origin Of Granite Landfroms In Chifeng,Inner Mongolia

Landforms developed on granite are recognized as granite landform.Currently,domestic researches on granite landforms are mainly about the exploitation of geomorphologic landscape resources and tourism.Meanwhile,specialized study on the formation mechanism and the evolutionary processes of granite landforms are rare.Therefore,this dissertation focused on the typical granite landforms in Chifeng,Inner Mongolia and seven landform areas,including Hongshan area,Arshihaty area,Pingding Mountain,Qing Mountain,Heilihe area,Qiguoshan Mountain,Bolongke area,were chosen.The research methodology covers field investigation,rock sampling,laboratory analysis and appraisal,systematic research on regional granite landforms with monographic research on typical granite landforms.All researches above provide a deeper understanding of geomorphic types,endogenic and epigene process of granite landfroms in Chifeng and the origin and evolution of typical granite landforms in this region.Achievements are described as follows.(1)A classification scheme on granite landform has been proposed,considering the combination of surface rolling,elevation and characteristics of granite landforms,which will lay a solid foundation for discussing its origin.(2)This paper detailedly studied the petrography,chronology and geochemistry of rock mass in the research area.Laboratory results show that six granite bodies invaded in Cretaceous while Hongshan granite formed in Devonian.Granite in aspects of trace elements showed a lack of Ba,Sr,P,Ti and Eu,and the tectonic environment discrimination diagrams presented that most granites belong to island-arc granites and plot to A-type granite.Base on the district geological analysis,the tectonic environment of the study area in late Mesozoic may convert to tension environment.(3)Geological controls in the origin and evolution of granite landforms in Chifeng reflected to fractures,especially joints,which play an important role in granite landform origin and evolution.Epigene forces mainly contain wind,fluviations,gravity and glaciations and acts in forms of weathering,erosion and transportation.In general,all forces work together and interact each other.The combination of fractures coordinating epigene process fundamentally controlled the distribution and geomorphic pattern of granite landforms.(4)The origin of three typical minor granite landforms was discussed.Ashihaty stone forest was created by deep weathering and exfoliation instead of glaciations.Bolongke boulders developed from corestones which separated by weathering and joints from the tors.According to the improved GMA method,the development of weathering pits in the Qing Mountain can be divided into six periods.By comparing with weathering pits developed in other regions,the age of weathering pits in the Qing Mountain was speculated to no older than 30 ka.And the number of weatheirng pits increased abruptly in the fourth period,showing a response to Holocene climate change.