Study On The Characteristics,evolution And Protection Of Volcanic Geological Relics In Nangong Geopark

With the development of science tourism,geotourism has come into fashion since the 21 st century,which brings about a good many geoparks that aim at scientific sightseeing and mass education in science,and in turn greatly promotes the scientific study and protection of a large number of precious geological relics across the country.As one sort of the most important geological relics,volcanic rock has become the research subject of numerous scholars.Nevertheless,a systematic study dealing with its formation mechanism and evolution model has not been accomplished by now.Generally speaking,the existing researches are mainly carried out from such single factor analysis as material foundation or tectonic conditions,which calls for an in-depth exploration of the comprehensive factors in terms of formation with a more mature and systematic research methodology.By means of current researches and field survey data,this thesis takes the volcanic rock geological relics in Nangong Mountain Geopark as research subject,and delves into the factors that contribute to its formation,including natural geographical conditions,regional geological background,and characteristics of petrology and geochemistry.In addition,this thesis divides the volcanic rock geological relics in Nangong Mountain into different categories and makes a detailed evaluation of each one based on the latest type research theory of geological relics.Besides,this thesis fulfills a systematic study upon the formation and evolution of the volcanic rock geological relics in Nangong Mountain by analyzing the activity mechanism of paleo-volcano,features of uplift and denudation,tectonic movement,basic material conditions and supergene process.Furthermore,this thesis focuses on a series of new ideas about the collapsed category of volcanic rock geological relics in Nangong Mountain as regards its formation mechanism,different phases of development,and the evolution model.(1)The volcanic rock geological relics in Nangong Mountain Geopark could be put into two major categories,viz.the collapsed category and the stone category,four sub-categories,and fifteen types.The collapsed category of volcanic rock receives the highest score among all the volcanic rock geological relics,and is the core of geological relics in this geopark.(2)This thesis makes a systematic analysis of the formation mechanism concerning the collapsed category of volcanic rock geological relics in Nangong Mountain,and arrives at a conclusion that this category is influenced by the following factors,ranging from tectonic background,material foundation,neotectonic movement,exogenic geological process to topography and physiognomy,and so on.Specifically,the basic formation condition lies in its binary stratum structure as well as the high and steep excavated slopes of a 45 degree angle;periodic tectonic uplift,hydrodynamic erosion,and supergene process like periglaciation in Himalayan period play an important role in controlling and transforming respectively;tectonic process after diagenetic stage remains the key factor after all.(3)This thesis proposes six development phases with reference to the collapsed category of volcanic rock geological relics,involving uplift,fragmentation,disintegration,collapse,accumulation and landslide.Accordingly,an evolution model of this category is constructed,which embodies five different grouping sequences.As a result of field survey,the most common grouping sequence goes like this,“volcanic rock ? volcanic rock bush ? volcanic rock screen ? volcanic rock forest ? secondary volcanic rock bush.” This sequence indicates its unique attributes of joints development and the content of calcareous cement in this region,and reflects its multiple cyclic feature of erosion as well.(4)Formed in the middle and late ages of early Silurian,the stone category of volcanic rock geological relics in Nangong Mountain is the outcome of continental margin rifting.After erupting from the paleo-volcanic edifice located in northeastern Shangyi Township via Hawaiian-Strombolian eruption type,the magma turns into rocks and becomes the final state through the rapid uplift in the middle and late ages of early Cretaceous,the slow uplift in the late Cretaceous-Miocene,and the superposition in the late tectonic movement.(5)The transformation as to the tone category of volcanic rock geological relics in Nangong Mountain could be divided into five phases approximately: the formation of folded basement and continental margin decomposition during the Mesoproterozoic and Neoproterozoic Era ? the transformation of passive continental margin rift basin during the late Sinian Epoch-Silurian Period ? the evolution of decoupling,nappe,strike-slip,deformation during the Hercynian-Yanshan Period ? the uplift reconstruction of fault blocks during the Himalayan Period ? the exogenic geological transformation during the Quaternary Period.(6)It is discovered that there are seventeen middle and small-sized geological disaster sites in Nangong Mountain area,among which the majority part is unstable landslide while the number of perilous rock avalanche and mud flow is comparatively low.In consideration of the potential disasters threatening the geological relics in Nangong Mountain area,this thesis puts forward the idea of building up classified geological protection zones and the strategy of EBG(namely,environmental capacity and building capacity of the geopark,and the establishment of geological relics landscape database).The volcanic geological relics in Nangong Mountain originate from the comprehensive effect combining various endogenic processes with exogenic processes.It is of great scientific and aesthetic value to have a correct understanding of geological relics in light of its formation and evolution,which also lays a solid foundation for reasonable protection and proper utilization in the future.