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Geochemical character of Neoproterozoic volcanic rocks in southwest Wales

Published online by Cambridge University Press:  01 May 2009

R. E. Bevins ,
T. C. Pharaoh ,
J. C. W. Cope  and
T. S. Brewer
R. E. Bevins
Affiliation:
Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF1 3NP, UK
T. C. Pharaoh
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
J. C. W. Cope
Affiliation:
Department of Earth Sciences, University of Wales, P.O. Box 914, Cardiff CF1 3YE, UK
T. S. Brewer
Affiliation:
Department of Geology, University of Leicester, Leicester LEI 7RH, UK
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Abstract

Volcanic rocks of Neoproterozoic age form several fault-related inliers in Wales and the Welsh Borderland. Those in North Wales and the Borderland have been investigated recently, while those in southwest Wales remain little studied. In southwest Wales, basic to intermediate lavas and related volcaniclastic rocks and silicic tuffs in the St David’s area comprise the Pebidian Supergroup, which is intruded by minor basic intrusions, while the Coomb Volcanic Formation, exposed farther east around Llangynog, is composed of basic and silicic lavas and silicic tuffs, intruded by a single dacite sill and numerous dolerite sills. New geochemical data show that both the Pebidian and Coomb basalts have subduction-related characteristics. The Coomb basalts are geochemically similar to those of the Uriconian Group of the Welsh Borderland, while the Pebidian basalts bear a similarity to volcanic rocks recovered from the Bryn-teg Borehole, in the Harlech Dome. Uriconian-type volcanic rocks may underlie much of the Midlands Microcraton, with the Welsh area underlain by volcanic rocks of Pebidian type.

Type
Articles
Information
Geological Magazine , Volume 132 , Issue 3 , May 1995 , pp. 339 - 349
Copyright
Copyright © Cambridge University Press 1995

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