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Distribution and tectonic setting of Ordovician K-bentonites in the United Kingdom

Published online by Cambridge University Press:  01 May 2009

W. D. Huff
Affiliation:
Department of Geology, University of Cincinnati, Cincinnati, OH 45221, U.S.A.
R. J. Merriman
Affiliation:
British Geological Survey, Keyworth, Nottinghamshire NG12 5GG, U.K.
D. J. Morgan
Affiliation:
British Geological Survey, Keyworth, Nottinghamshire NG12 5GG, U.K.
B. Roberts
Affiliation:
Department of Geology, Birkbeck College, University of London, London WC1E 7HX, U.K.

Abstract

Twenty-five Ordovician K-bentonite samples ranging in age from Llanvirn to Ashgill and representing both sides of the lapetus suture were analysed by INAA and XRF and compared on magmatic and tectonic discrimination diagrams. The proportional distribution of Nb, Y, Ti, Zr, Hf, Ta, Th and REE indicates that source volcanics were erupted in a setting that changed from subduction-related in the Llanvirn/Llandeilo to marginal basin extensional volcanism in the Caradoc/Ashgill. Welsh K-bentonites appear to be derived from volcanoes within the Welsh Basin, but K-bentonites from the Southern Uplands to not have characteristics consistent with a fore-arc setting, further suggesting a source related to ensialic marginal basin extensional volcanism.

Type
Articles
Copyright
Copyright © Cambridge University Press 1993

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