P71 インドネシア,テンガーカルデラ火山における巨大な火山体の形成時期(ポスターセッション)

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Tengger-Bromo volcano system has formed two calderas, Ngadisari and Sand Sea (Zaennudin, A. et al., 1994). K-Ar ages are obtained since our previous report (Toshida et al., 2012) to determine the age of the large aprons. The activity of Tengger volcano started with the formation of northern somma (Pananjakan) in 0.5-0.45 Ma, after the 1.2 m.y. hiatus following the formation of 1.7 Ma Kukusan volcano. Pananjakan is still the highest peak; repeated formations of shield volcanoes have added the aprons in the subsequent active periods. More than half of the edifice volume erupted between 0.35-0.2 Ma and have formed much of the aprons, with average eruption rate greater than 2km^3/ky. The northeastern to southern somma, and the edifice in northern apron, were formed in 0.35-0.3 Ma. The eastern apron and southwestern apron were formed in 0.25-0.2 Ma. Lavas and cones in the northwestern apron, and Ngadas basalt and andesite lavas, have formed in 0.08-0.06 Ma. The age of Sand Sea eruption is determined to be about 50 ka from stratigraphy relations. Therefore, the central cones are found to be younger than 50 ka, which is consistent to ^<14>C ages of tephra at the caldera rim (Takada et al., 2000). The average eruption rate of the central cone activity is calculated to be about 0.1 km^3/ky. Petrography and whole-rock chemistry of ejecta from the central cones, including the active vent (Bromo), are similar to those of Ngadas lavas and Sand Sea eruption PDC deposits. These observations imply that the present magma supply and accumulation system is similar to the one prior to the Sand Sea eruption.
2012-10-14

P71 インドネシア,テンガーカルデラ火山における巨大な火山体の形成時期(ポスターセッション)

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