Geochemistry of Late Caledonian Minettes from Northern Britain: Implications for the Caledonian Sub-Continental Lithospheric Mantle

Jason C. Canning, P. J. Henney, M. A. Morrison and J. W. Gaskarth
School of Earth Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
School of Earth Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Abstract: The geochemistry of late Caledonian minettes from across the orogenic belt is compared in order to constrain the composition of the Caledonian sub-continental lithospheric mantle (SCLM). All the minettes are similar petrographically and chemically and several samples have characteristics typical of near primary mantle melts. Samples from the Northern Highlands and the Caledonian foreland show enrichment in many trace elements (notably LILE and LREE) relative to those from the Grampians, the Southern Uplands and northern England, coupled with distinct Nd and Sr isotope characteristics. Processes such as fractional crystallization, crustal assimilation, and partial melting played a negligible role in creating the differences between the two groups which reflect long-term, time-integrated differences in the compositions of their SCLM sources. The Great Glen Fault appears to represent the boundary between these two lithospheric mantle domains. Other currently exposed Caledonian tectonic dislocations cannot be correlated directly with compositional changes within the SCLM. The chemical provinciality displayed by the minettes shows some resemblance to that within other late Caledonian igneous suites, including the newer granites, suggesting that the minettes may represent the lithospheric mantle contributions to these rocks.

Keywords: Caledonian • continental lithospheric mantle • minette • newer granites • Great Glen fault

Mineralogical Magazine; February 1996 v. 60; no. 398; p. 221-236; DOI: 10.1180/minmag.1996.060.398.15
© 1996, The Mineralogical Society
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