Collapse mechanism of the Paleogene Sakurae cauldron, SW Japan
Collapse mechanism of the Paleogene Sakurae cauldron, SW Japan
复制标题
日本西南部古近纪樱花大锅的塌陷机制
DOI：
10.1007/s00445-005-0036-3
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发表时间：
2006
影响因子：
3.5
通讯作者：
T. Arayashiki
中科院分区：
文献类型：
--
作者：
H. Komuro;M. Aoyama;T. Arayashiki
日本西南部古近纪樱花大锅具有多边形轮廓(21×13km2)的嵌套结构特征，包括一个圆形塌陷部分(直径5 km)。火山口填充体的总厚度为2000米，下部主要由长英质晶体凝灰岩和少量夹层安山熔岩流组成，上部由高品位的褐辉橄榄岩组成，顶盖有大型流纹质熔岩穹隆。这些成员分别代表第一阶段和第二阶段喷发。围绕着大锅边缘的断层包括相交的径向和同心断层，形成了这个大锅的多边形轮廓。因此，这个大锅的原生坍塌发生在一个多边形的火山口盆地，在那里积累了第一阶段喷发的产物。相反，内部塌陷部分由环状断裂系统定义。该地段的下沉与第二阶段喷发的高品位褐沸岩的堆积同时发生。因此，这种内圆坍塌代表了与顶峰喷发同时发生的同喷发下沉。第一阶段的岩浆排出作用可能导致顶板向外倾斜的环状断裂。随着钟形罩中心地块下沉，环形裂缝的打开导致大量浮石流动，导致岩浆迅速撤离，尽管岩浆压力可能在某种程度上有所下降。
The Paleogene Sakurae cauldron of SW Japan is characterized by a nested structure with a polygonal outline (21×13 km2) including a circular collapsed part (5 km in diameter). Total thickness of the caldera infill amounts to 2,000 m. The lower member of the infill consists mainly of felsic crystal tuff and lesser intercalated andesitic lava flows, whereas the upper member is composed of high-grade ignimbrite capped with a large rhyolitic lava dome. These members represent the first and second stage eruptions, respectively. Faults bounding the cauldron rim comprise intersecting radial and concentric faults, producing the polygonal outline of this cauldron. The primary collapse of this cauldron thus occurred as a polygonal caldera basin where products of the first stage eruption accumulated. In contrast, the inner collapse part is defined by a ring fracture system. This sector subsided concurrently with accumulation of the high-grade ignimbrite of the second stage eruption. This inner circular collapse thus represents syn-eruptional subsidence concurrent with the climactic eruption. Magma drainage during the first stage probably induced outward-dipping ring fractures in the chamber roof. Opening of the ring fractures following subsidence of the central bell-jar block caused rapid evacuation of magma as voluminous pumice flows, even though magma pressure may have decreased to some degree.