M.Sc. (Geology) / The study area is subdivided into seven tectonic domains, viz. Bandelierkop, Southern Beit Bridge Complex, Alldays, Hestern Transvaal, Soutpansberg, Waterberg and Lebombo domains. The Bandelierkop domain comprises the Southern Marginal Zone of the Limpopo Belt (Bdl) and the northern portion of the Kaapvaal craton (Bd2). Bdl is characterized by the presence of highly disrupted xenoliths of pelitic and mafic supracrustal rocks distributed in a "s ea " of granitic ·material. This contrasts with the much bigger supracrustal xenoliths in Bd2, i.e. the greenstone belt relicts. The granulite facies rocks of Bdl may have been upthrust roughly from south to north along one or more south-dipping thrust faults soling into a gently-dipping to flatlying basal shear zone. Since this model reveals the existence of the Kaapvaal craton partly on edge, the progressively higher grade of regional metamorphism (from greenschist to granulite facies) encountered in the Bandelierkop domain, from south (Bd2) to north (Bdl), could express the transition from upper crust to lower crust as exposed on the present land surface. The structural trends found in Bdl and Bd2 are not strictly confined to either area, and some overlapping exists. The most distinct structural trend in Bdl is a west-northwest fold trend, a northeast fold trend also being recognized in the eastern portion of Bdl. Bd2 exhibits f~ld trends varying from west-northwest to northeast in orientation; in this area there is ample evidence for the later nature of the northwest- to west-northwest oriented folding event. The east-northeast- to northeast folding is con~ dered to represent an event independent of the effect of deformation of the Kudus River shear zone to which this folding was previously thought to be related.The portion of the Central Zone of the Limpopo Belt falling within South African territory comprises the Alldays and Southern Beit Br_idge Compl ex (SBBCd) doma tn s., There exists a marked contrast between the roughly north trending fold trends of the Alldays domain and the east-northeast fold structure of the southernmost part of the Central Zone, the SBBCd. The relatively gentle plunges of the fold structure of the Alldays domain may have accentuated the size of the regional folds in this region. The SBBCd occupies a narrow east-northeast oriented strip extending immediately south of the Alldays domain, where tightly folded gneisses and metasedim~nts are exposed. all strata are strongly aligned in the regionally extensive eastnortheast direction. A contrasting difference between the SBBCd and the surrounding Precambrian terranes is clear, as the former domain conveys a relatively higher strain; this evidence of heterogeneous strain suggests that the SBBCd represents a shear zone. The shearing movement may have been of thrust type, consistent with the thrust model referred to above, and the SBBCd may be regarded as the thrust plane. In'iiew of the steeply-dipping, south-southwest oriented fold axes known to exist along part of the SBBCd (area south of Messina), it would appear that, at least in that area, the thrust movement would have been towards the north-northeast. A late, involved history of deformation followed in the SBBCd, during which one or more episodes of wrench-type movement may have taken place. The Soutpansberg domain is a relatively narrow and long fault zone of Proterozoic to Phanerozoic age that separates 'mobile belt' environment to the north, from 'cratonic' environment to the south. A linked fault system characterized by south-dipping, normal listric faults soling into ? gently-dipping major detachment surface may account for the structural pattern of this domain. The thrust system referred to above, which developed earlier in the geological history of the region along the Limpopo Belt - Kaapvaal craton boundary, may have controlled the late extensional displacement in the Soutpansberg domain. The overall structure of the Waterberg domain would seem to be controlled by the superimposition of northeastand northwest oriented gentle folds and, with the exception of locally intense deformation in the early Waterberg basin, would appear to have developed on a relatively stable portion of crust. The structure of the Lebombo domain is characterized by a north-south striking monocline with gentle east dip. Most of the lineaments inferred from the aeromagnetic survey of the study area originate from dyke intrusions. Faulting, fracturing and shearing are less clearly manifested in the pattern of the aeromagnetic contour maps, instead they are better correlated with the lineaments inferre~ from LANDSAT imagery and from the drainage patterns of the region.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:10717 |
| Date | 15 April 2014 |
| Creators | Chernicoff, Carlos Jorge |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
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