著者

和田 穣隆 南川 実咲

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.66, no.4, pp.281-291, 2021-12-31 (Released:2022-02-22)

参考文献数

23

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Surface structures of magmatic dikes reflect dike emplacement processes. Excellent exposures of the Miocene Hashigui-iwa dike (Wakayama, SW Japan) exhibit well-preserved surface structures including drag folds, scour marks, extension fractures, and cusps. Scour marks are evident on the drag-folded surface, and are in turn cut by extension fractures. Inside the cusps, which are clefts formed by adjacent convex margin irregularities, the drag-folded margins enclose mudstone lenses. Based on our field observations, we infer an emplacement mechanism whereby magma fingers ascended through moderately consolidated host sediments, forming scour marks on chilled margins and causing repeated drag folding. Continued magma flux allowed the fingers to expand, generating extension fractures on the chilled margins. Ultimately, the fingers coalesced, forming the now-preserved cusp structures.