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Corroded plagioclase feldspar inclusions in orthopyroxene and olivine of the Lower and Critical Zones, Western Bushveld Complex

Published online by Cambridge University Press:  05 July 2018

H. V. Eales ,
W. D. Maier  and
B. Teigler
H. V. Eales
Affiliation:
Department of Geology, Rhodes University, Grahamstown, South Africa
W. D. Maier
Affiliation:
Department of Geology, Rhodes University, Grahamstown, South Africa
B. Teigler
Affiliation:
Department of Geology, Rhodes University, Grahamstown, South Africa
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Abstract

The occurrence of spheroidal, ovoid or deeply embayed plagioclase inclusions within cumulus bronzite and olivine grains of both pyroxenites and norites here implies the existence of plagioclase feldspar in melts prior to the separation of ultramafic cumulates from these melts. Variations of Sr-isotope initial ratio are shown to exist within the feldspar populations of such rocks, even on a grain-to-grain scale. Five separate stratigraphic intervals within the Lower and Critical Zones exhibit this texture, and in each case these are intervals wherein normal fractionation trends (decline in both whole-rock and orthopyroxene Mg/(Mg+Fe2+); decline in Cr contents of orthopyroxene) became reversed. The data support a model for evolution of the texture during major episodes of influx of hot, primitive magmatic liquid into the chamber. Progressive mixing of the new liquid with resident liquids (bearing feldspar on the liquidus) effected progressive changes in the composition of the hybrid liquids produced, and resorption and imposition of reversed zoning upon the inclusions.

Keywords

Bushveld Complexmagma mixingresorptionplagioclase
Type
Research Article
Information
Mineralogical Magazine , Volume 55 , Issue 380 , September 1991 , pp. 479 - 486
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1991

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