Abstract
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.