Steep extrusion of late Archaean granulites in the Northern Marginal Zone, Zimbabwe: evidence for secular change in orogenic style

Blenkinsop, Thomas G., and Kisters, Alexander F.M. (2005) Steep extrusion of late Archaean granulites in the Northern Marginal Zone, Zimbabwe: evidence for secular change in orogenic style. In: Gapais, D., Brun, J.P., and Cobbold, P.R., (eds.) Deformation Mechanisms, Rheology and Tectonics: from minerals to the lithosphere. Special Publications of the Geological Society of London, 243 . Geological Society of London, London, U.K., pp. 193-204.

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Abstract

The Northern Marginal Zone (NMZ) of the Limpopo Belt in southern Zimbabwe is an essentially plutonic terrain, now consisting of granulite-gneisses, that was assembled by extensive magmatic under- and intraplating between ca. 2.7 and 2.6 Ga during late Archaean crustal shortening. In this study, we present the first evidence for regional-scale normal shear in the NMZ. Normal shear has been identified along an up to 500m wide, steeply dipping belt of mylonites, the Mtilikwe shear zone. Geochronologic and mineralogical-textural data indicate that normal shear occurred coeval with crustal shortening that was accommodated along gently-dipping thrust zones. The bulk strain pattern consisted of horizontal shortening, vertical stretching, and sub-vertical extrusion of a crustal segment. Horizontal shortening persisted throughout the orogenic evolution in the NMZ and no features typical of gravitational collapse in modern orogens are seen. This could imply that there was never major overthickening of the crust by thrusting, which may be a characteristic feature of Archaean orogeny.

Item ID: 677
Item Type: Book Chapter (Research - B1)
Keywords: tectonics, Archaean, extrusion, orogeny
ISBN: 978-1-86239-176-5
Date Deposited: 05 Oct 2006
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040303 Geochronology @ 50%
04 EARTH SCIENCES > 0403 Geology > 040312 Structural Geology @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
Citation Count from Web of Science Web of Science 5
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