[SIT32-P06] The magma system beneath Changbaishan Volcano, China: an insight from magnetotellurics imaging
キーワード：Changbaishan Volcanic field, magnetotellurics, magma chamber
The largest intraplate volcanic system in northeast Asia is the Changbaishan Volcanic Field in the Western Pacific Volcanic Belt approximately 1400 km from the Japan Trench, where the Pacific plate subducts beneath the Eurasian plate. The Changbaishan Volcanic Field is located on the northern edge of the Sino-Korean Craton, above a big mantle wedge. This stratovolcano is composed of an old basaltic shield, a young trachytic-to-rhyolitic cone, and a summit caldera. One of the two most violent eruptions in recorded human history occurred here between 920 and 960 AD and is known as the ‘Millennium Eruption’. The volcanic field experienced its most recent eruption in 1903 AD, followed by periods of unrest between 2002 and 2005. Concerns about increased activity made Changbaishan the focus of study for potential geologic hazards. Using magnetotelluric data collected from 2012 to 2014, we created a nearly linear N-S directional profile of the region across the Tianchi caldera in order to investigate the subsurface structure. A resistive crustal body is visible in the south part of the Changbaishan area in our three-dimensional model. Two successive magmatic conductors are beneath the Tianchi caldera less than 20 km from the surface. Petrologic analysis of comendite-trachyte from the Millennium Eruption indicates a formation from two different magmas and the double magmatic conductors are consistent with the geochemical model. Assuming the outermost resistivity of the magma body nearest to the surface is 25 Ω·m then it is located at a depth of 2 to 6 km and maybe responsible for recent volcanic earthquake events and ground deformation. Beneath the near surface magma chamber is a larger conductive magma body centered at an approximate depth of 15 km. This larger magma body maybe the main supply for the shallow magma system.