和歌山県三越峠付近の火砕岩岩脈の形成過程

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  • ワカヤマケン ミコシトウゲ フキン ノ カサイガンガン ミャク ノ ケイセイ カテイ
  • A Pyroclastic Dike, Mikoshi Pass, Wakayama Prefecture: Formation Process Inferred from Field and Laboratory Observations

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Abstract

A NW-SE trending telsic pyroclastic dike exposed at Mikoshi Pass, Wakavama prctecture, is described to infer its process of formation. This dike is composed of three zones I, II and III. The distinction among three zones is based on joint spacing and grain size. Zones I. II and III show wide, medium and narrow spacings of cooling joint, respectively, Averagc grain size of each zone decreases from I to III Zones I and II exist side by side, while zone III is contained in the upper part of zone II. This causes the upper part of the dike to be wide, and the growth of a horizontal fault consistent with the lower boundary of the zone III. Therefore, because the joint pattern of zone I is not symmetrical, and narrow spacing pattern near the dike wall is lacking in its zone II-side, zone II intruded between preexisting zone I and weakly, consolidated host rock, and zone I was eroded partly. After this event, zone III was intruded into zone II to push zones I and II away.

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