Stratigraphy and chronology of silicic tephras in the Shikotsu-Toya volcanic field, Japan: Evidence of a Late Pleistocene ignimbrite flare-up in southwestern Hokkaido
Stratigraphy and chronology of silicic tephras in the Shikotsu-Toya volcanic field, Japan: Evidence of a Late Pleistocene ignimbrite flare-up in southwestern Hokkaido
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DOI：
10.1016/j.quaint.2019.11.019
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发表时间：
2020-10
影响因子：
2.2
通讯作者：
M. Amma-Miyasaka;D. Miura;M. Nakagawa;S. Uesawa;R. Furukawa
中科院分区：
文献类型：
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作者：
M. Amma-Miyasaka;D. Miura;M. Nakagawa;S. Uesawa;R. Furukawa
位于日本北海道西南部的柴津-托亚火山场(STVF)包括三座破火山口火山(Toya、Kuttara和Shikotsu火山口及其后破火山口火山)和Yotei和Shiribetsu层状火山。对石卡里火山碎屑岩层的地层学、年代学、岩石学和玻璃地球化学进行了仔细的研究和重新评估。根据火山碎屑土层的存在和共同的岩石学特征，确定了单独的喷发幕，并通过与近端沉积的对比来识别每个特弗拉层的源火山。划分出28个喷发幕，其中6个是新发现的。根据北海道西南部中中新世以来活跃的喷流熔岩的K-Ar年龄，喷流安山质火山作用在北海道西南部中新世以来一直活跃，大约在0.9~0.5 Ma时汇聚在喷发熔岩中。在400KYR的休眠期之后，在托亚122.5 ka和120-115ka之前的Shiribetsu开始了爆炸性的喷发。约106ka的灾难性破火山口喷发导致了托亚破火山口的形成。爆炸活动随后向东迁移，库塔拉火山和四方火山分别在90ka和85ka之前开始爆发。随后，在大约75ka之后，在STVF的弧后一侧建造了大型层状火山Yotei。在这五座火山反复喷发后，最大的破火山口喷发发生在四国火山，约为43.8ka。自火山爆发以来，火山爆发指数(VEI*)每20-40KYR就有7次喷发，喷发的岩浆总量估计约为700 km3DRE(致密岩石当量)。这些发现表明，STVF是日本最年轻的褐沸石耀斑岩套之一，自125ka以来，其喷发速率约为5.6 km3DRE/Kyr。
The Shikotsu-Toya volcanic field (STVF) in southwestern (SW) Hokkaido (Japan) comprises three caldera volcanoes (Toya, Kuttara, and Shikotsu calderas and their post-caldera volcanoes) and Yotei and Shiribetsu stratovolcanoes. The stratigraphy, chronology, petrography, and glass geochemistry of tephra layers in the Ishikari pyroclastic terrain are carefully examined and reassessed. On the basis of the presence of volcaniclastic soil horizons and common petrological features, individual eruptive episodes are defined and the source volcanoes of each tephra layer are identified by correlation with proximal deposits. 28 eruptive episodes are distinguished, including six that are newly discovered. Based on K-Ar ages of older effusive lavas around the STVF, effusive andesitic volcanism, which was active since the Middle Miocene in SW Hokkaido, would have converged in the STVF by 0.9–0.5 Ma. After a dormant period of 400 kyr, explosive eruptions began at Toya 122.5 ka, and at Shiribetsu before 120–115 ka. A catastrophic caldera-forming eruption ca. 106 ka resulted in the formation of Toya caldera. Explosive activity then migrated eastward, and Kuttara and Shikotsu volcanoes began erupting explosively before 90 ka and 85 ka, respectively. Subsequently, the large stratovolcano Yotei was constructed after ca. 75 ka in the back-arc side of the STVF. Following repeated explosive eruptions of these five volcanoes, the largest caldera-forming eruption occurred ca. 43.8 ka at Shikotsu volcano. The STVF has produced VEI* (volcanic explosivity index) 7 eruptions every 20–40 kyr since explosive eruptions began, and the total volume of magma erupted in the STVF is estimated to be ca. 700 km3DRE (dense rock equivalent). These findings suggest that the STVF is one of the youngest ignimbrite flare-up suites in Japan, and that its eruption rate is up to ca. 5.6 km3DRE/kyr since 125 ka.