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Petrogenesis of Ordovician igneous rocks in the southern part of the Welsh Basin

Published online by Cambridge University Press:  01 May 2009

R. E. Bevins ,
G. J. Lees  and
R. A. Roacht
R. E. Bevins
Affiliation:
Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF1 3NP, U.K.
G. J. Lees
Affiliation:
Department of Geology, University of Keele, Keele, taffs ST5 5BG, U.K.
R. A. Roacht
Affiliation:
Department of Geology, University of Keele, Keele, taffs ST5 5BG, U.K.
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Abstract

During early Ordovician times volcanic and high-level intrusive activity occurred at numerous centres across North Pembrokeshire. Previous work suggested a geochemical transition in this activity from calcalkaline through to tholeiitic with time. However, new data indicate more extensive calc-alkaline magmatism and that both magma types were coeval. The origin of the calcalkaline magmas remains equivocal, but the tholeiitic magmas appear to have been derived from a source similar to N-type MORB, variably modified by supra-subduction zone fluids, combined with some fractionation during ascent. These data are consistent with emplacement in a supra-subduction zone marginal basin.

Type
Articles
Information
Geological Magazine , Volume 129 , Issue 5 , September 1992 , pp. 615 - 624
Copyright
Copyright © Cambridge University Press 1992

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