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The origin of Proterozoic massif-type anorthosites: Evidence from interactions between crustal xenoliths and basaltic magma

Dempster, T.J., Preston, R.J., and Bell, B.R. (1999) The origin of Proterozoic massif-type anorthosites: Evidence from interactions between crustal xenoliths and basaltic magma. Journal of the Geological Society, 156 (1). pp. 41-46. ISSN 0016-7649

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Abstract

Plagioclase-rich reaction zones occur around numerous aluminous crustal xenoliths within a suite of Palaeogene sub-volcanic basic sheets on the Isle of Mull, NW Scotland. The xenoliths consist of a glassy core, containing mullite needles, generated from the melting of pelitic source rocks. Thick plagioclase mantles grew at the interface between the aluminous liquid and the enclosing basaltic magma and provide a high-level analogue for the petrogenesis of Proterozoic massif-type anorthosites. Similar interactions between mantle-derived basic magmas ponded at the base of the crust and relatively Al-rich lower crustal lithologies would result in the precipitation of large volumes of plagioclase. Anorthosite massifs were then emplaced at higher crustal levels as crystal-rich mushes within relatively juvenile Proterozoic crust. The model negates the need to crystallize large volumes of mafic minerals prior to the production of plagioclase-saturated liquids, and also accounts for the significant influence of crustal sources on the isotopic signatures of all members of the anorthosite suite.

Item Type:Article
Status:Published
Refereed:Yes
Glasgow Author(s):Bell, Dr Brian and Dempster, Dr Tim
Authors: Dempster, T.J., Preston, R.J., and Bell, B.R.
Subjects:Q Science > QE Geology
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Journal of the Geological Society
Publisher:Geological Society of London
ISSN:0016-7649
Copyright Holders:Copyright © 1999 The Geological Society of London
First Published:First published in Journal of the Geological Society 156 (1) : 41 - 46
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher.

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