A structural and geochemical traverse across the NW outcrop of the Colenso Fault Zone, Saldanha, South Africa

Hamel, Kaylan

A structural and geochemical traverse across the NW outcrop of the Colenso Fault Zone, Saldanha, South Africa

Master Thesis

2016

Publisher

University of Cape Town

Department

Department of Geological Sciences

Faculty

Faculty of Science

Abstract

The Colenso Fault Zone marks the boundary between the Tygerberg and Swartland Terranes in the Pan-African Saldania Orogenic Belt. The fault zone comprises several discrete shear discontinuities that in places cross-cut relatively undeformed granites of the Cape Granite Suite. It is NW-SE striking, ~150 km long, and ~7km wide, but poorly exposed except in coastal exposures at the NW end. The deformation sequence can be divided into 2 sequences: The oldest deformation started with the emplacement of the G1, G2 and then the G3 of the Cape Granite Suite, followed by formation of aplite veins and strike-slip faulting generating cataclasites. The initial strike-slip sense of movement along the fault was sinistral, followed by dextral strike-slip shearing and finally late stage jointing. The Colenso Fault Zone is host to 3 large zones of cataclasis that are in the order of up to a few hundred metres in exposed down-dip and along-strike lengths. The cataclasites are composed of quartz and plagioclase clasts, in a phyllosilicate matrix. Both the wide cataclasites (several metres) and small cataclasite zones (tens of centimeters) show a decrease in shear intensity away from the core of the fault zone. The cataclasites have the same bulk chemical composition as the surrounding granite.

Keywords

Geological Sciences

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