Abstract

Six volcanic vents, trachybasaltic bosses, and new dykes replaced by kaolinite were discovered. The vents are built of trachybasaltic-trachytic and basaltic plugs and of tuffisites and tuffs. In the trachybasalts, plagioclase and anorthoclase display complicated reaction phenomena, reflecting changes in crystallization conditions. The trachybasaltic and trachytic bodies were emplaced first and subsequently were altered to kaolinite (upper Jurassic). Magmatic activity was resumed after an intense erosion period leading to the formation of the vents and of the lower Cretaceous basaltic volcanic complex which was in part extruded through these vents.

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