Abstract

Ordinary General Meeting 21 October 1970 at 5.00 p.m.

The Twenty-fifth William Smith Lecture: A return to William Smith, was delivered by Professor W. S. Fyfe, F.R.S., Royal Society Professor of Geochemistry in the University of Manchester, in the Wellcome Lecture Theatre at the apartments of The Royal Society.

Ordinary General Meeting 11–12 November 1970

A two-day Discussion Meeting: Volcanism and the structure of the earth, arranged jointly by the Volcanic Studies Group of the Geological Society, and The Royal Society, organized by Professor J. Sutton, F.R.S., Dr P. S. Sabine & Dr R. R. Skelhorn, was held in the apartments of The Royal Society.

The following papers were read (* denotes the speaker):

1. Aspects of magmatic evolution on Reunion Island By W. J. Wadsworth* and B. G. J. Upton

The ‘primitive’ shield lavas of the two Reunion volcanoes are olivine-tholeiites whose compositions are dictated by olivine addition or subtraction, down to a limiting value of approximately 5% MgO. They differ from those of Hawaiian shields (a) in being more alkalic and (b) in containing dunite-wehrlite-gabbro nodule suites. The elder of the two has a ‘Kohala-like’ structure with a veneer of more highly differentiated volcanic rocks. These, ranging from feldsparphyric basalts to trachytes, are dominantly hypersthene-normative with more extreme compositions carrying modal quartz. Fractionation of basic feldspar (An85) and diopsidic pyroxene, as well as olivine, is believed to have controlled the low pressure evolution of the differentiated lavas. The differentiated magmas were (a) less siliceous and (b) slightly

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