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The Silurian volcanic rocks of the Mendip Hills, Somerset; and the Tortworth area, Gloucestershire, England

Published online by Cambridge University Press:  01 May 2009

P. C. van De Kamp
P. C. van De Kamp
Affiliation:
Shell Development Co., P.O. Box 481, Houston, Texas, 77001.
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Summary

Field, petrographic and chemical studies on the Silurian volcanic rocks of the Mendip Hills show that there are probably 15 or more rock units in the series including andesite and rhyodacite lavas, rhyodacite tuffs, agglomerates, and a dolerite dyke. The predominant rock type is rhyodacite which may be as much as 80 percent of the volcanics. Volcanics of Silurian age from the Tortworth area, Gloucestershire, are of latite-andesite composition.

The Mendip rocks have been deuterically altered. Calcite-quartz-laumontite veins are common in fractures in these rocks. The agglomerates are particularly susceptible to weathering and some bombs are extensively altered to clays. Twelve rocks were chemically analysed for 36 elements each. No anomalous base metal concentrations were found in the volcanics although Pb, Zn, and Cu mineralisation is known in the area. K/Rb varies from 202 to 909 in these calc-alkaline rocks.

Type
Articles
Information
Geological Magazine , Volume 106 , Issue 6 , December 1969 , pp. 542 - 553
Copyright
Copyright © Cambridge University Press 1969

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References

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