Study On The Quaternary Volcanic Apparatus And Cause Of The Pyroclastic In Longgang Region, Jilin Province

The Longgang volcanic cluster territory is large, and the activity is exquisite, the volcanism is complicated;the magmatic erupted, the phreatomagmatic erupted and the phreatic erupted alternately. According to the clear geologic relation and information related about the isotope, the Neozoic volcanic activity can be divided into 10 stages. According to the history of the colcanic cluster and eruption process, the explosive activities' feature is phreatomagmatic erupted and magmtic erupted alternately. But in the certain volcano's depositional succession, we can see the phreatic eruptional matter-phreatomagmatic eruptional matter-magmatic eruptional matter depositional succession. According to the cause of formation, form, and the deposit's structure, the volcanic edifices includes Haw aiian, St rombolian, sub-Plinian, maar, and composite types.Based on the fractal theory, we analyze the fractal features of the grain size of pyroclasts. Our results show that the fractal dimension of the pyroclasts of phreatomagmatic eruption is smaller than that of the phreatic eruption, but greater than that of the magmatic eruption. The values of fractal dimension can be used as parameters to distinguish different type of volcanic eruption. The phreatic eruption pyroclastic materials are wall rock, the magmatic eruption pyroclastic materials are magma, there are chaps on the surface of the phreatomagmatic eruption pyroclastic materials. The Quaternary explosive activities involve magmatic explosions, phreatomagmatic explosions and phreatic explosions. Magmatic explosions. The different explosive activities can form a volcano alone, and form a volcano alternately. The components, depositional structure, granularity, and configuration of the different explosive activities' production are distinguishable different. The volcanic hazards in Longgang region are descendent scoria, coulee and base-surge deposits. The hazard of descendent scoria is superficial hazard, the radius is 9 kilometers. The hazard of the coulee is zonal, the region is about 6-9 kilometers. The radius of the hazard of the base-surge deposits is about 4 kilometers.