Volcaniclastic Ejecta,Volcanostratigraphy And Volcanic Geological Mapping In Changbaishan Tianchi Volcanoes

Volcanic lava and volcaniclastic ejecta cover most of Tianchi and its adjacent areas in Changbaishan.The distribution characteristics and volcanostratigraphy characteristics of volcaniclastic ejecta in the area are complex.This article mainly from pyroclastic distribution characteristics,petrology,geochemistry and accumulation model,filling pattern,structural layer six aspects volcaniclastic ejecta and volcanostratigraphy of Changbaishan area is studied,and based on the basic geological map Changbaishan area,although the geological map has much defect,but can provide convenience for research scholars,also provide some scientific basis for decision-making of local government.There is a little regular change from the near to the far distance from Tianchi crater of Changbaishan.The near source accumulation is mainly yellow pumice,the middle source accumulation is mainly black pumice,and the far source accumulation is mainly white pumice.With the increase of distance,the separation and rounding of pumice debris become better.With the increase of the distance,the content of carbon debris decreases and the content of bedrock debris increases,which may be the result of the transportation of pyroclastic.According to the geochemical analysis of the fine pyroclastic(volcanic ash)and the lavas in the Qixiangzhan,it can be indicated that the volcaniclastic ejecta and lava of Changbaishan-Tianchi may originate from the differential evolution of mantle-derived magma,which was mixed with the crustal components during the upwelling.Its forming environment is a non-orogenic intraplate stretching environment.The volcanostratigraphy in the Changbaishan area has complex construction processes,such as eruptive period,lithologic composition,and complex relationships,which increase the difficulty of gaining an overall understanding of the volcanostratigraphy.Based on previous research and our field geological survey,the complex volcanostratigraphy of the Changbaishan area can be divided into four filling pattern types from bottom to top.They are lava flows filling in valleys,lava flows filling in platform,lava flows formed the cone,and pyroclastic flow filling in crater or valleys.The following are the details.Annular fault is developed in Changbaishan-Tianchi and radially distributed outwards.The faults are mainly NE and NW in the area.The pyroclastic accumulation area can be divided into three types according to the accumulation mode:The area of air fall accumulation is mainly in the NE of Changbaishan-Tianchi,which is as far as Japan;The pyroclastic flow accumulation area is mainly distributed elliptically within a radius of 50 km around Changbaishan-Tianchi;The lahar accumulation area is mainly distributed along the Erdaobai river,which can be divided into fine clastic pumice lahar accumulation and coarse clastic rock block lahar accumulation.From the bottom to the top,the structural layer includes pre Cenozoic structural layer,Cenozoic structural layer and Millennium eruption structural layer.According to the faults,the pyroclastic accumulation area and the structural layer,the 148×110km area of Changbaishan was preliminarily mapped.