Abstract

Report of a meeting held in Burlington House on 28 November 1985. The meeting was convened by K. Coe, and chaired by W. S. Pitcher and M. Brown, morning and afternoon sessions respectively.

A special scientific meeting of the Society was held on Thursday 28 November 1985, with the title Geochemical aspects aspects of granite and related rocks. From the papers offered, ten were selected which dealt with data and concepts derived from British and Irish granitic bodies.

One exception to this was the first contribution, presented by R. Macdonald. In this it was proposed that because of late crystallization and subsolidus processes, plutonic granites may not record magmatic chemistry. Macdonald and his co-workers suggested that silicic obsidians, rhyolites and acid ash-flow sheets may be better indicators of original composition, implying that these extruded rocks are the chemical equivalents of unmodified granitic liquids. This precept was used in interpreting data derived mainly from the Western Cordillera to show that compositions of source rocks were in some cases more important than the tectonic setting of the magma.

The second paper, by D. A. C. Manning, emphasized the importance of the volatiles B, F, Li and P in granites, manifest in familiar ‘accessory’ minerals and exerting controls on various aspects of the melt, including its emplacement mechanism. Other trace and some major element abundances correlated with these indicating a genetic relationship. A lower crust source for the volatiles was suggested.

Two papers followed on the younger and older granites of the

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