Abstract

The Belleoram stock of homogeneous adamellite is a shallow, late-orogenic intrusion emplaced in arkosic conglomerates, granite, intermediate to basic lavas, and clastic sedimentary rocks. The intruded rocks range in age from Cambrian to Late Devonian. Salic dykes and minor faults cutting the stock represent the closing phases of orogenic activity in this area.Structural, petrographie, and chemical data indicate that the stock is of magmatic origin. Differential assimilation of the host conglomerate and shales may have locally modified the composition of the crystallizing magma. Field observations and modal analyses show that arkosic conglomerates near the stock have been altered to rocks of granitic composition. The margin of the stack has been basified near contacts with shale. Xenoliths of shale have been altered to compositions approaching that of their host. Hydrothermal experiments show that under appropriate conditions the magmatic vapour phase could transport soda, potash, alumina, and silica, in amounts sufficient to explain the observed compositional variation.These results suggest that under suitable conditions combined processes of autometasomatism and assimilation may be an important factor in granitization and basification at the margins of shallow intrusions.

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