Tephrochronological Study on the Shikotsu and Kuttara Volcanoes in Southwestern Hokkaido, Japan
Tephrochronological Study on the Shikotsu and Kuttara Volcanoes in Southwestern Hokkaido, Japan
复制标题
日本北海道西南部支笏火山和久多罗火山的年代学研究
DOI：
10.5026/jgeography.103.268
复制
发表时间：
1994
影响因子：
3.1
通讯作者：
K. Yamagata
中科院分区：
文献类型：
--
作者：
K. Yamagata
在北海道西南部的支笏火山和库塔拉火山的周边地区以及石狩低地，覆盖着厚厚的晚更新世火山碎屑沉积物。根据岩相变化，将这些火山碎屑沉积物划分为不同的沉积单元。因此，每个单元不一定代表一次喷发。在本文中，一次喷发的产物火山灰岩（火山碎屑岩组）被认为是最适合指示平静期的"火山灰土壤"，因为它的沉积速率低，具有普遍性。（En-c和Spfl·Spfa 1; Spfa 7、8、9和10）被重新解释为代表两次喷发的产物，因为其中没有火山灰土。新发现三个火山碎屑层。石狩低地晚更新世火山碎屑沉积由22个火山灰组组成，分布在库塔拉火山周围的火山碎屑沉积又细分为12个火山灰组和1个火山渣群。Kuttara火山喷发火山碎屑岩建造自下而上依次为：Kt-8、7、6、5、4、Kt-Hy、Kt-3、Kt-Tk火山渣群、Kt-2、Kt-1。Kt-8... -1主要由大、中型爆发形成的普利尼亚浮岩流沉积和浮岩流沉积组成，本文尝试用几种岩石学参数和地层位置对库塔拉火山周边地区和石狩低地的火山碎屑岩组进行对比。以下火山碎屑岩地层彼此相关：Kt-8和Aafa 1，Kt-5和Mpfa 2b，Kt-4和Mpfa 2a，Kt-3和Spfa 4，Kt-Tk和Spfa 3，Kt-1和Spfa 2。此外，还证实了Kt-7、Kt-Hy、Nj-Os等火山碎屑岩建造向石狩低地的扩展。支笏火山在一次大规模破火山口形成喷发（Spfl·Spfa 1：Ca. 32 ka），并经过短暂的休息时间，目前后火山活动开始。Kuttara火山在70 - 40 ka期间经历了7次爆发，之后的成层火山是由Kt-Tk火山渣群喷发形成的，最后的两次爆发（Kt-1和Kt-2）形成了山顶破火山口。
The surrounding area of the Shikotsu and the Kuttara volcanoes, and Ishikari-Lowland, in the southwestern Hokkaido, are covered with thick pyroclastic deposits of the late Pleistocene. These pyroclastic deposits have been subdivided into units according to facies changes. consequently each unit does not necessarily represented a single eruption. In the present paper, the products of one eruption (tephra formations) are separated from one another by recognition of intervening “volcanic ash soils” which are considered to be the most suitable for indicating quiet period, owing to its low depositional rate and generality.In the Ishikari-Lowland, the previously defined two groups of tephra formations (En-c and Spfl · Spfa 1; Spfa 7, 8, 9 and 10) are reinterpreted to represent the products of two eruptions, because the volcanic ash soils are absent among them. And three tephra formations are newly recognized. Twenty two tephra formations constitute the late Pleistocene pyroclastic deposits in the Ishikari-Lowland.The pyroclastic deposits distributed around the Kuttara volcano are subdivided into twelve tephra formations and one scoria fall group. The tephra formations derived from the Kuttara volcano are as follows in ascending order : Kt-8, 7, 6, 5, 4, Kt-Hy, Kt-3, Kt-Tk scoria fall group, Kt-2, Kt-1. The Kt-8 …-1 are mainly composed of plinian pumice fall deposits and pumice flow deposits generated by large and moderate scale explosive eruptions.The correlation of the tephra formations in the surrounding area of the Kuttara volcano and the Ishikari-Lowland is attempted with several petrographic parameters and stratigraphic position. The following tephra formations are correlated each other : Kt-8 and Aafa 1, Kt-5 and Mpfa 2b, Kt-4 and Mpfa 2a, Kt-3 and Spfa 4, Kt-Tk and Spfa 3, Kt-1 and Spfa 2. In addition, it is proved that the following tephra formations spread to the Ishikari-Lowland : Kt-7, Kt-Hy, Nj-Os.On the Shikotsu volcano, three explosive eruptions preceded a large scale caldera forming eruption (Spfl · Spfa 1 : Ca. 32 ka), and after a short repose time, present post caldera activity started. The Kuttara Volcano was the site of seven explosive eruptions during the period from 70-40 ka ; then the stratovolcano was formed by erupting Kt-Tk scoria fall group, and the summit caldera was formed by the last two explosive eruption (Kt-1 and 2).