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

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doi: 10.1144/gsjgs.156.1.0041
Authors:Dempster, T. J.; Preston, R. J.; Bell, B. R.
Author Affiliations:Primary:
University of Glasgow, Department of Geography, Glasgow, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, Vol.156(Part 1), p.41-46. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:1999
Note:In English. 42 refs.; illus., incl. 1 table, sect.
Summary: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.
Sections:Petrology
Subsections:Igneous petrology
Subjects:Anorthosite; Basaltic composition; Cenozoic; Chemical composition; Crust; Crystallization; Emplacement; Feldspar group; Framework silicates; Genesis; Geochemistry; Igneous rocks; Inclusions; Magmas; Paleogene; Petrography; Plagioclase; Plutonic rocks; Precambrian; Proterozoic; Reaction rims; Silicates; Tertiary; Upper Precambrian; Xenoliths; Argyllshire Scotland; Europe; Great Britain; Hebrides; Inner Hebrides; Mull Island; Scotland; United Kingdom; Western Europe; Strathclyde region Scotland
Coordinates:N561500 N564000 W0054000 W0063000
Abstract Numbers:99M/2141
Record ID:1999019864
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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