Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Surface and core samples of finely porphyritic rhyolite and associated tuffs from the Inyo volcanic chain have been divided up into three groups on the basis of Na, Fe and some immobile trace elements (Co, Sc, Th, U, REE, etc.). These groups were produced by mixing of two compositionally different magmas derived from different magma chambers. Field relationships suggest that the first magma to be intruded along the fracture was from a source in the south. The other finely porphyritic magma was intruded later from a source to the north. Mixing probably occurred within the feeder system during intrusion. Finally a coarsely porphyritic magma was intruded into the dike from another chamber, probably to the south. One of the finely porphyritic magma groups has a differentiation trend within the group that can be best explained by fractional crystallization of a mixture of minerals, probably dominated by feldspars and magnetite, with removal of up to 17% solids. Boron appears to have been lost from devitrified rocks in the intrusive part of the chain, but not from similar rocks in the flow. This loss may have been caused by variations in the accessibility of fluids in these environments or differences in the degree and timing of differentiation. It appears that boron was not lost during the degassing of the magma that accompanied emplacement of the flows. Therefore, the degassing process was not an equilibrium process with respect to boron.