Characteristics Of Volcano Building And Geological Mapping In Changbaishan-tianchi Volcano And Adjacent Area

Over Twenty boreholes with depths ranging from tens of meters up to 4500 m have been drilled in the Changbaishan-Tianchi volcano and adjancent region since the year of2000,aiming at the volcano stratigraphy,geothermal and petroleum interests.The wells drilled through from the surface of the millennium eruption deposits to the Archean basement rocks.The data reveals that there are five stratigraphic formations related to the evolution of the Changbaishan volcanos.The upward vertical sequence is(1)Pre-Cenozoic basement including Archean metamorphic rocks and granite,Proterozoic granite,Cambrian-Ordovician shale,marl and limestone,Triassic granite,Jurassic andesite and silica clastic rocks,Cretaceous rhyolite and sedimentary rocks.(2)Miocene to Pleistocene flood basalt interbedding with lake deposits,shield and dome building of trachyte,andesite and basalt.(3)Pleistocene to Holocene cone-building of pantellerite,obsidian,welded ignimbrite and red basaltic scoria.(4)The Millennium Eruption of fallout and pyroclastic deposits which occurred during 946 CE.(5)Fallout and pyroclastic deposits and reworking deposits following the last giant eruption.We have studied 238 outcrops and 20 borehole sections during 2006-2021.This new data base provides us with 258 controlling points on the rocks’ assemblage and other geological features provided by the previously published literatures since 1961.This is the first time for us to map the five formations together in the same plan veiw.We hope to show the possible basement influence on the features of the ChangbaishanTianchi volcanos.It is interesting to see from the map that The Cenozoic volcanic lava and volcaniclastic deposits are mingled with the pre-Cenozoic rocks in the map,and that lahar deposits are stream related,and the widespread pumiceous soils are closely related to the millennium eruption deposits in compotition.