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On the nature of the parental magma of the Palaeogene Staffa Magma sub-type, Isle of Mull, Scotland

Published online by Cambridge University Press:  03 November 2011

Andrew C. Kerr
Andrew C. Kerr
Affiliation:
Department of Geology, University of Leicester, University Road, Leicester LEI 7RH, U.K.
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Abstract

The tholeiitic, columnar (Staffa type) lavas found at, and near, the base of the Tertiary lava succession on the Isle of Mull contrast markedly with overlying transitional tholeiiticalkalic Mull Plateau Group lavas, and as a result previous workers have classed the Staffa type lavas as a distinct group. The Staffa type lavas are among the most contaminated in the British Tertiary Igneous Province and have equilibrated and fractionated at shallow depths within the crust (relative to the overlying Plateau Group lavas), so obscuring the chemical identity of their parental magma. However, Staffa type lavas which are more basic than examples hitherto reported help in the elucidation of the parental magma. It is demonstrated that the Staffa type lavas were derived from a parental magma which was compositionally similar to that of Plateau Group lavas. The primary reasons for the distinctive features of the Staffa type are related to post-mantle melt generation processes, i.e. to extensive crystal fractionation and to crustal contamination at shallow crustal depths. The lavas are compositionally and temporally unrelated to the Hebridean tholeiitic magma types, the Central Mull Tholeiite type and the Skye Preshal More type.

Keywords

basaltHebridesmantle
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 89 , Issue 2 , 1998 , pp. 87 - 93
Copyright
Copyright © Royal Society of Edinburgh 1998

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