Abstract

The Cap d'Ours Complex in the Rouyn area, previously named the Glenwood Rhyolite, includes three types of rhyolitic volcanoclastites. Pyroclastites make up approximately half of the volcanoclastites; they are characterized by deposits with poor stratification and massive appearance, by aphanitic or pumiceous porphyric rhyolite blocks and lapilli, and by an association with variable proportions of pumice and shards. They seem to result from accumulated laminar flows similar to debris flows. The alloclastites form about one third of the volcanoclastites; they show several features common to the pyroclastites (stratified appearance, graded bedding, mixed source materials). However, some key parts of the outcrop indicate fragmentation in place, supporting the interpretation of a dome fragmented in situ and partially reworked. The autoclastites make up the remaining volcanoclastites. They are represented by flow breccia characterized by a progressive transition from a fragmented to a massive rhyolite. The Cap d'Ours Complex rhyolites form an arrangement of volcanoclastic components much more complex than described previously. In a single site occupying less than graphic, there are at least three types of volcanoclastites formed by different volcanic processes as varied as the eruption of pyroclastic and magmatic flows, and the injection and destruction of a dome or a spine. [Journal Translation]

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