流紋岩浅所貫入岩体の内部構造と貫入過程 : 佐賀県泉山陶石鉱床における流紋岩体の例

概要

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The Izumiyama porcelain stone deposit is hosted by a rhyolite intrusion and is located in the Saga prefecture of southwestern Japan. The Izumiyama deposit is currently being exploited and thus provides an excellent opportunity to observe the internal structure of the rhyolite intrusion. The rhyolite intrusion is oval in shape, having dimensions of approximately 400 m in length and 200 m in width. This is a main body, hereafter referred to as R1. R1 contains flow structures in a 20 to 30 m-wide zone which defines the margins of the body. At least, 5 small oval-shaped bodies (R2-R6) occur within R1. R2 to R6 also contain margins of flow structures and brecciated cores. The occurrence of R2 to R6 within R1 implies that the latter was emplaced first with continued magmatic activity being responsible for the emplacement of the smaller intrusions. Field evidence suggests that earlier formed margins of flow stmctures were brecciated and incorporated into the rising magma within the cores of the intrusions. These features may be characteristic of small, nearsurface rhyolitic intrusions. NE-trending cracks are considered to represent degassing structures of the intrusions. Late developed normal faults subparalelled to the cracks, resulting in the formation of a graben structure on the top. Finally hydrothermal alteration resulted in the cracks and faults being filled with clay minerals.
特定非営利活動法人日本火山学会の論文
1994-07-20