Changbaishan-Tianchi(CBS-TC)is a giant composite active volcano,which is well-known by its intense eruptions(946～947AD)and unrest during 2002-2006.Since Late Pleistocene,CBS-TC has experienced several intense eruptions of highly differentiated comenditic and trachytic magma with SiO2＞65％.According to geophysical research,there are shallow crustal magma chambers below Tianchi.However,the magmatic system of the historical eruptions remains unconstrained.In this paper,massive glass compositions from electron microprobe analysis are applied to constrain the detailed pressure condition of the Tianchi magma storages by using the Qz-Ab-Or trinary projection,the Clinopyroxene Machine Learning geobarometer and the rhyolite-MELTS geobarometers.Among the Late Pleistocene volcanic products,the Tianwenfeng(TWF)eruption,the Qixiangzhan(QXZ)eruption,the Millennium comenditic eruption(ME-I)and the Millennium trachytic eruption(ME-Ⅱ)yield pressure ranges of 246～444MPa,184～344MPa,162～314MPa and 438～540MPa,respectively.After pressure-depth transformation,the four episodes of silicic magma are generally supposed to be stored in upper to middle crust level.It is worth-noting that the pressure ranges of TWF,QXZ and ME-I comenditic magma have a trend of descent with eruption time,which might reveal the evolution process of an identical comenditic magma chamber to a shallower level in a 10-thousand-year timescale;while the trachytic magma chamber generating the ME-Ⅱ eruption is located in a lower layer beneath the former one.The new findings derived from our work are helpful in understanding the evolution of the Tianchi magma chamber system,explaining volcanic monitoring data and forecasting of volcanic hazards.
关键词
长白山天池火山/地质压力计/高分异岩浆/岩浆贮存压力/岩浆演化/岩浆房系统
Key words
Changbaishan-Tianchi volcano/Geobarometer/Highly differentiated magma/Storage pressure/Magma evolution/Magma chamber system
维普
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