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Mineralogical data on a multiple intrusion in the Rustenburg Layered Suite of the Bushveld Complex

Published online by Cambridge University Press:  05 July 2018

G. Davies  and
R. G. Cawtnorn
G. Davies
Affiliation:
Nuclear Physics Research Unit, University of the Witwatersrand, Jan Smuts Avenue, Johannesburg 2001, South Africa
R. G. Cawtnorn
Affiliation:
Department of Geology, University of the Witwatersrand, Jan Smuts Avenue, Johannesburg 2001, South Africa
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Abstract

Mineralogical and chemical data are presented on an intrusion of a hypersthene gabbro body into coarse-grained noritic cumulates of the critical zone, which occurs at the margin of the Rustenburg Layered Suite of the Bushveld Complex. Two types of contact relations are found between the above two rock suites: (1) a clearly cross-cutting contact is observed on the southern margin of the hypersthene gabbro body close to the interface between the layered suite and the floor rocks; (2) a diffuse heterogeneous contact is found on the north-western limb of the body which is further into the complex. Field observations and chemical data suggest that, at the time of the hypersthene gabbro injection, the surrounding cumulates were above ambient temperatures. The difference in the contacts described above is probably related to the prevailing temperature gradient at the time of emplacement. The cumulate rocks further into the complex were at a higher temperature than those closer to the margin.

Trace element chemistry and phase relations in the basalt tetrahedron indicate that the hypersthene gabbro is genetically unrelated to the cumulate rocks which it intrudes. The body probably represents an offshoot of the magma from which the upper zone of the Rustenburg Layered Suite crystallized.

Type
Research Article
Information
Mineralogical Magazine , Volume 48 , Issue 349 , December 1984 , pp. 469 - 480
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1984

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Footnotes

*

Present address: NBRI, CSIR, PO Box 395, Pretoria 0001, South Africa.

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