阿蘇火砕流堆積物中のプルアパート構造と本質レンズのしぼり出し現象

概要

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Densely welded tuff of the Aso-3 pyroclastic flow, deposited in a deep valley, 5 km to the east of the southeast corner of the Aso caldera, shows various features of deformation accompanied with welding. During welding disruption or parting of the welded layer was caused by differential compaction and secondary flowage and left nearly vertical gap, 70 to 150 cm in width. Numerous essential lenses, collapsed pumices or scoriae, have been squeezed out from walls of the gap and some of them bent down. A part of the once-opened pull-apart gap has closed again by plastic flow of more fluidal horizon in the welded layer. Some essential lenses, having vertically elongated secondary vesicles, were pulled apart by nearly vertical tension. The squeeze-out of essential lens indicates lower viscosity of lenses than matrix. Similar phenomena often observed in welded tuffs are denser welding of lenses than matrix, micro-intrusion from lenses into matrix along foliation and localization of pull-apart displacement in lenses.
特定非営利活動法人日本火山学会の論文
1983-07-01