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Journal of the Geological Society; 2001; v. 158; issue.4; p. 653-664
© 2001 Geological Society of London

Regular Article

Tabular intrusion and folding of the late Archaean Murehwa granite, Zimbabwe, during regional shortening

TOM G. BLENKINSOP & PETER J. TRELOAR

1 Department of Geology, University of Zimbabwe, PO Box MP 167, Mount Pleasant, Harare, Zimbabwe (e-mail: tgb{at}icon.co.zw)
2 Centre for Earth and Environmental Sciences Research, School of Earth Sciences and Geography, Kingston University, Penrhyn Road, Kingston upon Thames, Surrey KT1 2EE, UK

Scientific editing by Rob Strachan.

The Murehwa granite belongs to the late Archaean Chilimanzi suite of granites that occupy more than 50% of the Zimbabwe craton. The granite has compositional layers on metre to tens of metre scales with generally shallow dips, and dip directions towards the centre of the granite near its margins. The layering is systematically folded about sub-horizontal east–west axes. Microcline phenocrysts are generally strongly aligned parallel to the layering, but locally crosscut the layering because they are axial planar to the folds. Crystals are not significantly deformed: fabrics are thus magmatic. The granite was intruded in a tabular sheet that may have been only about 6 km thick and fed by dykes, contrary to previous concepts of diapirism/ballooning for some Archaean granites of the Zimbabwe craton. The systematic orientation of magmatic folds and axial planar fabrics demonstrate that the granite was intruded during regional north-south shortening. This shortening is consistent with the orientation of cratonic-scale fractures that were intruded by the Great Dyke within 25 Ma of the intrusion of the Murehwa granite. The granite may have intruded in a relatively short interval of less than 1–26 Ma, within the longer duration of the entire Chilimanzi granite event.


Keywords: granites, intrusions, magmatic fabric, folding, crustal shortening.




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