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Stressed pyroxenite nodules from the Jagersfontein kimberlite

Published online by Cambridge University Press:  05 July 2018

G. D. Borley  and
P. Suddaby
G. D. Borley
Affiliation:
Dept. of Geology, Imperial College of Science and Technology, London, S.W.7
P. Suddaby
Affiliation:
Dept. of Geology, Imperial College of Science and Technology, London, S.W.7
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Summary

Examination of some pyroxenite nodules from the Jagersfontein kimberlite shows that they have suffered variable deformation followed by different degrees of recovery. Most interes~ting of the nodules is the 'diallage rock', which consists of highly sheared and broken lamellar crystals of diopside containing exsolved enstatite. Petrographic evidence indicates a pre-tectonic exsolution of enstatite and a syntectonic exsolution of pyrope-almandine from enstatite. Deformation occurred in the mantle, prior to incorporation of the nodule in the kimberlite. Compositions of pyroxenes from the diallage rock suggest it re-equilibrated at a temperature of 1000° and at a pressure of about 35 kb. Olivine and phlogopite, accompanied by serpentine, occur only in broken kink-bands in the diallage rock and they are considered to be of secondary origin, precipitated from kimberlite magma at temperatures near 700°

Type
Research Article
Information
Mineralogical Magazine , Volume 40 , Issue 309 , March 1975 , pp. 6 - 12
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1975

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