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Pumpellyite-dominated metadomain alteration at Builth Wells, Wales–evidence for a fossil submarine hydrothermal system?

Published online by Cambridge University Press:  05 July 2018

R. E. Bevins
R. E. Bevins*
Affiliation:
Department of Geology, National Museum of Wales, Cardiff, CF1 3NP, Wales
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Abstract

Two metamorphic alteration styles have been observed in basic lavas and volcaniclastic rocks of the Builth Volcanic Series of Ordovician age exposed at Llanelwedd Quarry, in the Builth lnlier, Wales. The first alteration style is characterized by the development of a mineral assemblage comprising albite+chlorite+ sphene+ pumpellyite ± prehnite ± calcite ± white mica, although original textures are largely preserved. This alteration pattern corresponds with that developed in volcanic and volcaniclastic rocks elsewhere in Wales, and which is attributed to the effects of burial. The second alteration style is characterized by the development of metadomains dominated by pumpellyite or, more rarely, prehnite. In the metadomains no original textures are seen in hand specimen. This alteration pattern has, so far, not been observed elsewhere in Wales, and it is here suggested that it might result from a submarine hydrothermal circulation system.

Keywords

pumpellyitemetadomainsmetamorphismBuilth WellsWales
Type
Research Article
Information
Mineralogical Magazine , Volume 49 , Issue 352 , June 1985 , pp. 451 - 456
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1985

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