The Granulite-Facies Rocks of the Limpopo Belt, Southern Africa

Reenen, Dirk D. van; Roering, C.; Brandl, G.; Smit, C. A.; Barton, J. M.

doi:10.1007/978-94-009-2055-2_14

Cited by 34 publications

(32 citation statements)

References 31 publications

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“…The BBC is composed of predominantly leucocratic quartzo-feldpathic gneiss, quartzite and marble with intercalated metapelitic gneiss, magnetite quartzite and mafic granulites (e.g. [Coward, 1983], [Watkeys et al, 1983] and [Van Reenen et al, 1990]). The well-developed metamorphic and deformational characteristics of the BBC obscure the sedimentological and stratigraphic relationships between these lithologies (e.g.…”

Section: The Central Zonementioning

confidence: 99%

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A review of the pressure–temperature–time evolution of the Limpopo Belt: Constraints for a tectonic model

Rigby

Mouri

Brandl

2008

Journal of African Earth Sciences

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Published literature argues that the Limpopo Belt can be subdivided into three zones, each with a distinctive geological character and tectono-metamorphic fingerprint. There are currently two contrasting schools of thought regarding the tectono-metamorphic evolution of the CZ. One camp argues that geochronological, structural and prograde pressure-temperature (P-T) evidence collectively indicate that the CZ underwent tectono-metamorphism at ca. 2.0 Ga which followed a clockwise P-T evolution during a transpressive orogeny that was initiated by the collision of the Kaapvaal and Zimbabwe cratons. Deformation and metamorphism consistent with this scenario are observed in the southern part of the NMZ but are curiously absent from the whole of the SMZ. The opposing view argues that the peak metamorphism associated with the collision of the Kaapvaal and Zimbabwe cratons occurred at ca. 2.6 Ga and the later metamorphic event is an overprint associated with reactivation along Archean shear zones. Post-peakmetamorphic conditions, which at present cannot be convincingly related to either a ca. 2.6 or 2.0 Ga event in the CZ reveal contrasting retrograde paths implying either nearisothermal decompression and isobaric cooling associated with a 'pop-up' style of exhumation or steady decompression-cooling linked to exhumation controlled by erosion. Recent data argue that the prograde evolution of the ca. 2.0 Ga event is characterised by isobaric heating prior to decompression-cooling. Contrasting P-T paths indicate that either different units exist within the CZ that underwent different P-T evolutions or that some P-T work is erroneous due to the application of equilibrium thermobarometry to mineral assemblages that are not in equilibrium. The morphology of the P-T path(s) for the ca. 2.6-2.52 Ga event are also a matter of dispute. Some workers have postulated an anticlockwise P-T evolution during this period whilst others regard this metamorphic event as following a clockwise evolution. Granitoid magmatism is broadly contemporaneous in all three zones at ca. 2.7-2.5 suggesting a possible causal geodynamic link. P-T contrasts between and within the respective zones prevent, at present, the construction of a coherent and inter-related tectonic model that can account for all of the available evidence. Detailed and fully-integrated petrological and geochronological studies are required to produce reliable P-T-t paths that may resolve some of these pertinent issues.

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Section: The Central Zonementioning

confidence: 99%

“…Similarly, the Southern Marginal Zone (SMZ) is separated from the Kapvaal Craton (KC) by the northwards dipping Hout River Shear Zone (HRSZ) (e.g. [Van Reenen et al, 1990] and ). The NMZ and SMZ are commonly regarded as granulite-facies equivalents of the Archean granitegreenstone successions which prevail in the adjacent cratons (e.g.…”

Section: Introductionmentioning

confidence: 99%

A review of the pressure–temperature–time evolution of the Limpopo Belt: Constraints for a tectonic model

Rigby

Mouri

Brandl

2008

Journal of African Earth Sciences

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“…Similarly, the Southern Marginal Zone (SMZ) is separated from the Kaapvaal Craton (KC) by the northwards-dipping Hout River Shear Zone (e.g. Van Reenen et al, 1990;Smit et al, 1992). The NMZ and SMZ are commonly regarded as granulite-facies equivalents of the Archean granitegreenstone successions which prevail in the adjacent Zimbabwe and Kaapvaal Cratons (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Conversely, the CZ forms a lithologically diverse and distinct supracrustal sequence, which includes the Beit Bridge Complex (BBC), a diagnostic supracrustal unit composed of predominantly leucocratic quartzo-feldspathic gneiss, quartzite and marble with intercalated metapelitic gneiss, magnetite quartzite and mafic granulites (e.g. Watkeys et al, 1983;Brandl, 1983;Van Reenen et al, 1990). The CZ also contains several suites of tonalitic, trondjhemitic and granodioritic (TTG) orthogneiss, including the Sand River Gneiss (SRG) and the Alldays Gneiss (AG) (e.g.…”

Section: Introductionmentioning

confidence: 99%

Conflicting P–T paths within the Central Zone of the Limpopo Belt: A consequence of different thermobarometric methods?

Rigby

2009

Journal of African Earth Sciences

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a b s t r a c tA single metapelitic sample from the Verbaard locality, near Messina was investigated in order to construct a P-T path and moreover, highlight pertinent contradictions in the current P-T database. Interpretations based on P-T pseudosections, garnet isopleth thermobarometry and mineral mode/isopleth modelling indicate that the mineral assemblages, textures and zonations developed in the metapelite formed along a single clockwise P-T path. The metamorphic evolution is characterized by an early high-pressure phase at 10-11 kbar/800°C, followed by a simultaneous pressure decrease and temperature increase to $8/850°C and subsequent retrogression via decompression-cooling to 4-5 kbar at T < 650°C. Growth zoning in garnet provides evidence for an earlier, prograde history, however, as potential melt-loss was not accounted for this must be deemed speculative. The results of this study agree entirely with that of [Zeh, A., Klemd, R., Buhlmann, S., Barton, J.M. 2004. Pro-and retrograde P-T evolution of granulites of the Beit Bridge Complex (Limpopo Belt, South Africa); constraints from quantitative phase diagrams and geotectonic implications. Journal of Metamorphic Geology 22, 79-95], who adopted a similar approach to thermobarometry i.e. pseudosections. The results are, however, inconsistent with recent publications that argue for a twofold, metamorphic history defined by two decompression-cooling paths (DC1 $2.6 Ga and DC2 $2.0 Ga) that are separated by an isobaric heating path ($2.0 Ga). The disparity in the results obtained from different workers can be explained by an examination of the thermobarometric methods employed. The methodology employed to derive the twofold, polymetamorphic P-T path appears to be erroneous. At present, the most reliable and robust method for determining P-T paths is the pseudosection approach to thermobarometry. Future modelling of Limpopo Belt granulites should adopt this strategy and ensure potential melt-loss is taken into account. Alternatively, this potential problem can be avoided altogether by investigating rocks of mafic composition.

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“…Considering their widespiead distribution in space and time, the petrogenesis of this association is important to the evolution, differentiation and maturation of the continental crust (e.g. Brown, 1983;Kenah & Hollister, 1983;van Reenen et al, 1990).…”

Section: Introductionmentioning

confidence: 99%

Ductile shearing and migmatization at mid‐crustal levels in an Archaean high‐grade gneiss belt, northern Gallatin Range, Montana, USA

Mogk

1992

Journal Metamorphic Geology

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A high-grade Archaean gneiss terrane in the northern Gallatin Range, south-western Montana, USA, contains a trondhjemite-tonalite gneiss (TTG) sequence that was migmatized during pervasive ductile shearing. Metamorphism of these rocks is in the upper amphibolite to granulite facies at temperatures of 680-735 "C, pressures in excess of 8 kbar, and a 'clockwise' P-T-t path is inferred. Ductile shearing occurred in metre-scale anastomosing bands of high strain throughout the area. The TTGs have been extensively migmatized via vapour-present melt reactions involving the incongruent melting of biotitebearing TTG to produce hornblende and granitic melt. The granitic melt is produced in narrow envelopes adjacent to ductile shear zones in response to infiltration of water-rich solutions. Melt migration occurred on a local scale, and extraction of melt from the system left behind a plagioclase-hornblende residuum with minor interstitial microcline. Ductile shearing and migmatization in the TTG operated in a positive feedback mechanism; the entire volume of gneiss was chemically and mechanically reworked through the cyclical infiltration of aqueous solutions, vapour-present melting and melt-enhanced deformation. The proposed melt reaction may be an important crustal differentiation process considering that (1) many collisional orogens d o not attain temperatures high enough to permit vapour-absent melting, (2) pervasive networks of ductile shear zones at mid-crustal levels may serve as channels for fluid ingress and melt extraction, and (3) the large volumes of TTGs in Archaean and Phanerozoic orogens may constitute a significant source reservoir for certain types of high-level granites.

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The Granulite-Facies Rocks of the Limpopo Belt, Southern Africa

Cited by 34 publications

References 31 publications

A review of the pressure–temperature–time evolution of the Limpopo Belt: Constraints for a tectonic model

A review of the pressure–temperature–time evolution of the Limpopo Belt: Constraints for a tectonic model

Conflicting P–T paths within the Central Zone of the Limpopo Belt: A consequence of different thermobarometric methods?

Ductile shearing and migmatization at mid‐crustal levels in an Archaean high‐grade gneiss belt, northern Gallatin Range, Montana, USA

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