Pliocene voluminous volcanism and tectonics in Southern Kyushu

久津火山区是九州南部一条从西北到东南长约100公里、宽约25公里的弧形带。晚中新世至中更新世火山活动可分为三个阶段。寿津火山岩分为低钾安山岩和高钾安山岩。在第一阶段，低钾安山岩出现在西部，高钾安山岩出现在东部。在第二阶段，高钾安山岩广泛爆发，整个地区。第三阶段，低钾安山岩在西侧再次喷发，高钾安山岩在东侧再次喷发。此外，寿津火山岩的母岩浆来源于高钾高镁安山岩、低钾高镁安山岩和拉斑玄武岩三种岩浆。在南九州之下， 关于我们 艾德形成于晚中新世至近代岛弧型地幔之下。岛弧型地幔是由古俯冲洋壳和沉积物的碎块以及俯冲前板片的含水流体交代的地幔楔等组成。如果软流圈部分熔融程度较低，则形成板内型碱性玄武岩岩浆。在大程度部分熔融的情况下，产生板内型拉斑玄武岩岩浆。碱性玄武岩和拉斑玄武岩岩浆与岛弧型地幔反应，分别形成高K_2O和低K_2O高镁安山岩岩浆。在这一过程中，玄武岩岩浆获得俯冲特征，岩浆中SiO_2含量增加。高镁安山岩岩浆的分离结晶作用形成了体积庞大的二辉安山岩。此外，具有岛弧特征的玄武岩岩浆似乎是岛弧型地幔部分熔融的产物，这一模式也可以解释九州新生代火山活动的特征。少

The Hisatsu volcanic province is a across arc belt of about 100km in length from northwest to southeast and 25km wide in Southern Kyushu. The volcanic activity, occurred in the period from late Miocene to middle Pleistocene, is divided into three stages. The Hisatsu volcanic rocks are classified into low-potassium (low-K) and high-potassium (high-K) andesites. In the first stage, the low-K andesites occurred in the west side of the province and the high-K andesites in the east side. In the second stage, the high-K andesite erupted widely all through out the area. In the third stage, the low-K andesite erupted in the west side again, and the high-K andesite in the east side. Further, the Hisatsu volcanic rocks were derived from three kinds of parental magma, high-K high-magne-sian andesite, low-K high-magnesian andesite and tholeiite magmas.The following is a plausible model for the origin of the Hisatsu Volcanism. Beneath the southern Kyushu, the fertile and hot asthenosphere has exist … More ed under the island arc type mantle from late Miocene to recent. The island arc type mantle is estimated to be composed of the fragments of the ancient subducted oceanic crusts and sediments, and the mantle wedge metasomatized by the hydrous fluid from previously subducted slabs, etc. When the asthenosphere ascends to shallow part of the mantle, it begins to melt. If the degree of the partial melting of the asthenosphere is small, within-plate type alkali basalt magma is formed. In case of large degree of partial melting, within-plate type tholeiite magma is produced. If the alkali basalt and tholeiite magmas reacts with the island arc type mantle, the high and low K_2O high-magnesian andesite magmas are formed, respectively. In this process, basalt magma acquires the subduction signature and SiO_2 in the magma increases. The fractional crystallization of the high-magnesian andesite magmas formed the voluminous two pyroxene andesites. Further, basalt magma with island arc signature seems to produce by the partial melting of the island arc type mantle.This model can also explain the characteristics of the Cenozoic volcanism in Kyushu. Less