The lithospheric mantle and lower crust-mantle relationships under Scotland: A xenolithic perspective

Author(s)
B. G. J. Upton, H. Downes, L. A. Kirstein, Constanza Bonadiman, P. G. Hill, Theodoros Ntaflos
Abstract

In the British Isles the majority of volcanic rocks containing upper mantle and lower crustal xenoliths occur in Scotland. Most of the occurrences are of Carboniferous-Permian age. This paper presents new data on the mineral chemistry of spinel lherzolite xenoliths from the five principal Scottish tectonic terranes. Compositional variations among the minerals emphasize the broad lateral heterogeneity of the subcontinental lithospheric mantle across the region. The remarkable range of Al2O3 v. CaO exhibited by the clinopyroxenes compared with data from other 'xenolith provinces' emphasizes the extremely complex tectonomagmatic history of the Scottish lithosphere. The generalized age increase from southern and central Scotland to the Northern Highland and Hebridean terranes of the north and NW, with concomitant complexity of geological history, is reflected also by trace element and isotopic studies. Reaction relationships in lherzolites from the Hebridean Terrane, owing to pervasive metasomatism, involve secondary growth of sodic feldspar. This, and light REE enrichment of clinopyroxenes, points to involvement of a natro-carbonatitic melt. Most pyroxenitic xenoliths are inferred to form a basal crustal layer with a generally sharp discontinuity above the underlying (dominantly lherzolitic) mantle. A second discontinuity is inferred to separate these ultramafic cumulates from overlying, broadly cognate metagabbroic cumulates. © The Geological Society of London.

Organisation(s)
Department of Lithospheric Research
External organisation(s)
University of Edinburgh, University of London, Universitá degli studi di Ferrara
Journal
Journal of the Geological Society
Volume
168
Pages
873-886
No. of pages
14
ISSN
0016-7649
Publication date
2011
Peer reviewed
Yes
Austrian Fields of Science 2012
105105 Geochemistry, 105120 Petrology
Portal url
https://ucrisportal.univie.ac.at/en/publications/c94de0b2-885f-4ddf-8404-b317f2683f77