PETROGRAPHY AND MECHANISM OF ERUPTION OF ARCHEAN DALEMBERT TUFF, ROUYN-NORANDA, QUEBEC, CANADA

The petrography of the Dalembert tuff, an assemblage of pyroclastic flows was investigated in two sections named the Dalembert and Reneault sections. Tuffs in the Dalembert section consist of pumice, plagioclase crystals, and a polymict assemblage of lithic fragments probably derived from sub-aerial lavas. The features suggest the eruption of overflowing glowing avalanches, and emplacement of the cold tuff under the sea. It is suggested that the eruption began with formation of an overflowing glowing avalanche from a fissure on a volcanic island.