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Rare earth element, Sr- and Nd-isotope evidence for petrogenesis of Permian basaltic and K-rich volcanic rocks from south-west England

Published online by Cambridge University Press:  05 July 2018

R. S. Thorpe ,
M. E. Cosgrove  and
P. W. C. van Calsteren
R. S. Thorpe
Affiliation:
Department of Earth Sciences, the Open University, Milton Keynes, MK7 6AA, UK
M. E. Cosgrove
Affiliation:
Department of Geology, the University, Highfield, Southampton, SO5 9NH, UK
P. W. C. van Calsteren
Affiliation:
Department of Earth Sciences, the Open University, Milton Keynes, MK7 6AA, UK
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Abstract

Permian basic/ultrabasic lavas from south-west England may be divided into a ‘basaltic’ and a K-rich group. Both groups have enrichment of large-ion lithophile (LIL) elements relative to high field strength (HFS) elements, and the K-rich group show large degrees of LIL enrichment (c.50–500 times primordial mantle) in association with varied transition element concentrations. Samples from both groups 87Sr/86Sri = 0.704–0.705 and 143Nd/144Ndi = 0.5123–0.5127 and plot close to the mantle array on an ɛSr−ɛNd diagram. These data are interpreted in terms of derivation of the lavas from magmas resulting from partial melting of mantle which had experienced less (for the basaltic group) or more (for the K-rich group) enrichment in LIL elements as a result of migration of mantle melts. Such enrichment accompanied or followed subduction of oceanic lithosphere below south-west England. The resultant magmas experienced fractional crystallization of olivine and pyroxene prior to eruption.

Keywords

rare earth elementsstrontium isotopesneodymium isotopesPermian lavassouth-west England
Type
Petrology
Information
Mineralogical Magazine , Volume 50 , Issue 357 , September 1986 , pp. 481 - 489
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1986

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