Rare Earth Element, Sr- and Nd-Isotope Evidence for Petrogenesis of Permian Basaltic and K-Rich Volcanic Rocks from South-West England

R. S. Thorpe1, M. E. Cosgrove2 and P. W. C. van Calsteren1
1 Department of Earth Sciences, the Open University, Milton Keynes, MK7 6AA, UK
2 Department of Geology, the University, Highfield, Southampton, SO5 9NH, UK

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 ɛSrɛNd 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 elements • strontium isotopes • neodymium isotopes • Permian lavas • south-west England

Mineralogical Magazine; September 1986 v. 50; no. 357; p. 481-489; DOI: 10.1180/minmag.1986.050.357.11
© 1986, The Mineralogical Society
Mineralogical Society (www.minersoc.org)