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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Post-caldera explosive activity inferred from improved 67-30 ka tephrostratigraphy at Aso Volcano, Japan
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Post-caldera explosive activity inferred from improved 67-30 ka tephrostratigraphy at Aso Volcano, Japan

机译：由日本麻生火山的67-30 ka岩相地层学改进推断出火山口后的爆炸活动

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摘要

An improved 67-30 ka tephrostratigraphy for Aso Volcano in southwestern Japan can be used to reconstruct the eruptive history during most of the post-caldera activity of the volcano. The thick tephra sequence preserved atop the Aso pyroclastic-flow deposits around the caldera mainly comprises mafic scoria-fall and ash-fall deposits, because basaltic to basaltic andesitic magmas have been dominant at Aso Volcano. Previous studies have identified 36 silicic pumice-fall deposits that act as valuable beds for correlation of the complicated tephra sequence. In addition to the twelve pumice-fall deposits previously identified, the present study has newly recognized 17 tephra units, denoted Nakakubo tephra 17 to 1 (NbT17-NbTl) in ascending order, in the stratigraphic sequence between 67 and 30 ka. Overall, explosive mafic eruptions were more common than explosive silicic eruptions. Explosive eruptions occurred frequently in the period 67-50 ka, but happened only infrequently in 50-30 ka. Between 50 and 31 ka, silicic and mafic tephra volumes were both relatively small, but multiple explosive silicic eruptions occurred at 31-30 ka, and the 30 ka catastrophic Kusasenrigahama eruption, which was the largest eruption in the post-caldera stage of Aso Volcano, discharged voluminous magma (1.1 km~3) as a pumice-fall deposit. Individual tephra discharge volumes were relatively small (<0.57 km~3) during the periods when explosive eruptions were frequent, whereas large amounts of magma were discharged after the long quiescent period of about 20,000 years in the case of both silicic and mafic eruptions. The reconstructed tephrostratigraphy and chemical characteristics of tephras during the period between 67 and 30 ka suggest a magma plumbing system model in which mafic magmas were steadily intruded from the mantle to the lower crust, and silicic magmas generating explosive pumice eruptions were produced by crustal anatexis due to heating of the crust by mantle-derived mafic magmas beneath Aso Volcano in the post-caldera stage.
机译：日本西南部的阿苏火山经过改进的67-30 ka岩相地层学，可以用来重建火山大部分火山口后活动期间的喷发史。保存在火山口周围的阿苏火山碎屑流沉积物顶部的厚特非拉层序主要包括镁铁质鳞屑沉积和灰分沉积，因为在阿苏火山中玄武岩至玄武质安山岩浆占主导地位。先前的研究已经确定了36个硅质浮石秋天沉积物，它们是与复杂的特非拉序列相关的有价值的床。除了先前确定的十二个浮岩沉积矿床外，本研究还新发现了17个地弗拉单位，以67至30 ka的地层顺序升序表示为Nakakubo tephra 17比1（NbT17-NbT1）。总体而言，爆炸性铁镁质喷发比爆炸性硅质喷发更为普遍。爆炸性喷发在67-50 ka期间频繁发生，但在50-30 ka时很少发生。在50至31 ka之间，硅质和铁镁质特菲拉的体积都相对较小，但在31-30 ka发生了多次爆炸性硅质喷发，而30 ka灾难性的库萨森格里哈玛火山喷发是阿苏火山火山口后阶段的最大喷发。排出的大量岩浆（1.1 km〜3）为浮石沉积物。在硅灰岩和镁铁质岩浆喷发频繁爆发期间，个别的提夫拉火山喷出量相对较小（<0.57 km〜3），而在经过约20,000年的长期静止期后，大量岩浆被排出。在67至30 ka期间重建的球墨岩的地层学和化学特征提出了一种岩浆管道系统模型，其中铁镁岩浆稳定地从地幔侵入到下地壳，硅酸盐岩浆产生了地壳苯甲酸，产生了爆炸性浮石喷发。在火山口后阶段，由阿苏火山下面的地幔派生的镁铁质岩浆加热地壳。

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