Characterization and correlation of the Hegawa‐Kasamori 5 tephra, a widespread tephra aged c . 450 ka associated with large‐scale pyroclastic flows from southern Kyushu, SW Japan
Characterization and correlation of the Hegawa‐Kasamori 5 tephra, a widespread tephra aged c . 450 ka associated with large‐scale pyroclastic flows from southern Kyushu, SW Japan
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Hekawa-Kasamori 5 火山灰的特征和关联，这是一种分布广泛的火山灰，年龄约 450 ka，与日本西南部九州南部的大规模火山碎屑流有关。
DOI：
10.1002/jqs.3172
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发表时间：
2019
影响因子：
2.3
通讯作者：
Suzuki Takehiko
中科院分区：
文献类型：
--
作者：
Nishizawa Fumikatsu;Suzuki Takehiko
中更新世广泛分布的Tephra，这里定义为Hegawa-Kasamori 5 tephra(Hgw-Ks5)，在日本的大片地区被新发现。在日本西南部九州南部近岸地区发现了与HGW-Ks5的共褐煤火山灰沉积(CAFD)有关的大规模火山碎屑流沉积。HGW-KS5可能起源于九州南部的艾拉火山口，广泛分布于距震源1000多 公里的本州岛卡萨森组的沉积物中。在火山喷口西北部地区，火山灰岩以非焊接的火成岩的形式稀疏分布，并以地层的形式暴露在著名的小林-鹿森火山灰岩之上。通过岩石学特征、玻璃碎屑的主要元素地球化学和斜方辉石的折射率对HGW-Ks5进行了表征。前人的地层同位素研究结果表明，Hgw-Ks5的喷发年龄为434-458ka(海相同位素第12期)。假定来自火山口的CAFD呈同心分布，根据分布面积和CAFD厚度估算出HGW-KS5的视体积为~100CAFD· ~3。因此，Hgw-Ks5喷发的火山爆炸性指数为7。
A Middle Pleistocene widespread tephra, defined here as Hegawa‐Kasamori 5 tephra (Hgw‐Ks5), has been newly recognized over a broad area of Japan. Large‐scale pyroclastic flow deposits associated with co‐ignimbrite ash fall deposits (CAFDs) of Hgw‐Ks5 have been identified in the proximal southern Kyushu area, south‐west Japan. Hgw‐Ks5 possibly originated from the Aira caldera in southern Kyushu, and it is widely spread and intercalated with deposits of the Kasamori Formation, Honshu Island, more than 1000 km away from the source. In the north‐west area of the Aira Caldera, the tephra is sparsely distributed in the form of non‐welded ignimbrites, and is exposed stratigraphically above the well‐known Kobayashi‐Kasamori tephra. Hgw‐Ks5 is characterized through petrographic features, major element geochemistry of glass shards, and refractive indices of orthopyroxene. The results of previous stratigraphic isotope studies indicate that the eruptive age of Hgw‐Ks5 is 434–458 ka (Marine Isotope Stage 12). Assuming that the CAFDs originating from the Aira Caldera are distributed concentrically, the apparent volume of Hgw‐Ks5, estimated from the area of distribution and CAFD thickness, is ~100 km3. Therefore, a volcanic explosivity index of 7 is assigned to the Hgw‐Ks5 eruption.