CONVECTION AND CRYSTALLIZATION IN THE CRIFFELL-DALBEATTIE PLUTON

It is argued that the asymmetric Dalbeattie granodiorite-granite pluton developed as a result of convectional circulation in the magma chamber during the consolidation of the outer xenolith-bearing granodiorite shell. The shell was deformed by the intrusion of aplite veins, the development of a penetrative foliation, and the emplacement of dykes with chilled margins due to the intermittent uprise of the magma body which eventually consolidated as granite. A porphyrite-porphyry series of dykes provides information concerning the degree of crystallization of the magmas that existed in the pluton the final stages of its emplacement and consolidation. Oscillatory zoning in plagioclases can be explained by constitutional supercooling or by changes occurring during convection. The effects of crystal fractionation and diffusion within the pluton are discussed. © 1981 The Geological Society.