An investigation of archean and paleoproterozoic metamorphic processes in the Limpopo belt via detailed analysis of reaction textures in metapelites from the Bandelierkop Formation, Southern Marginal Zone of the Limpopo belt
| dc.contributor.advisor | Stevens, Gary | en_ZA |
| dc.contributor.author | Madlakana, Nonkuselo | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. | en_ZA |
| dc.date.accessioned | 2021-11-23T09:01:57Z | |
| dc.date.accessioned | 2021-12-22T14:34:21Z | |
| dc.date.available | 2021-11-23T09:01:57Z | |
| dc.date.available | 2021-12-22T14:34:21Z | |
| dc.date.issued | 2021-12 | |
| dc.description | Thesis (PhD)--Stellenbosch University, 2021. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: The well exposed granulite facies rocks in the Southern Marginal Zone (SMZ) of the Limpopo Belt (LB), South Africa, represent an exceptional window into the lower crust where partial melting processes can be directly observed and investigated. Previous studies have demonstrated that these rocks experienced a single granulite facies metamorphic event at ca. 2.71 Ga under conditions of ~850 ᵒC and 11 kbar along with partial melting via a sequence of biotite incongruent melting reactions, which produced melt together with peritectic garnet, orthopyroxene, cordierite, sillimanite and plagioclase. In rare cases, peritectic garnets host an abundance of euhedral plagioclase inclusions with variable compositions. Despite their potential that they present in understanding details of the melting processes they have not been a focus of a previous study. This thesis focuses on these inclusions in order to understand the anatectic processes responsible for the generation of the metasedimentary migmatites in the SMZ, and importantly also characterises their retrograde metamorphic history. Specifically, this work integrates geochemical, geochronological and petrological investigations of metapelitic granulites from two localities in the Bandelierkop Formation (the Bandelierkop quarry and the Brakspruit quarry), where Neoarchean high-grade metamorphic textures have been preserved. Electron beam microanalysis show that some of the euhedral plagioclase inclusions have high anorthite content (up to An83) compared to the majority of plagioclase inclusions, as well as the matrix plagioclase, in these rocks. This is interpreted to reflect disequilibrium melting of plagioclase in the source due to slow diffusion in plagioclase. The variable composition of these euhedral plagioclase crystals suggests their entrainment by the melt from different localised domains and the entrapment at the sites where peritectic garnet was growing from the melt. The preservation of these garnets must be due to rapid and efficient melt loss from the residual source, possibly aided by short residency of these granulites at high temperature due to fast exhumation. The peak metamorphic assemblage is partially retrogressed under amphibolite facies conditions. The detailed petrological investigations of the retrogressed metapelitic granulites, combined with LA-ICP-MS dating on rutile suggests that the SMZ of the LB has experienced a previously unrecognised Paleoproterozoic regional amphibolite facies event. This Paleoproterozoic event is 600 Myrs younger than the age of peak metamorphism in the SMZ. Within the Kaapvaal Craton, it relates to the ca. 2.15 Ga U-Pb age from metamorphic monazite and titanite in the Ghaap group, Chuniespoort Group and the Pretoria Group of the Transvaal Supergroup and the ca. 2.1 monazite age from the Central Rand Group of the Witwatersrand, all of which have been interpreted to indicate craton-scale fluid flow associated with thrusting and folding in the Kaapvaal Craton. Globally, the ca. 2.15 Ga event correlates to the ca. 2.22–2.15 Ga tectonic driven fluid flow and the Ophthalmain orogeny in the Pilbara Craton in Western Australia. It can be concluded that the SMZ of the LB, is a polymetamorphic terrain, with an older granulite facies anatectic metamorphic event at ca. 2.71 Ga and a younger amphibolite facies Paleoproterozoic overprint at ca. 2.1 Ga. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. | af_ZA |
| dc.description.version | Doctoral | en_ZA |
| dc.format.extent | xvii, iv, 163 pages : illustrations (some color), maps | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/124005 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Limpopo Belt (South Africa and Zimbabwe) | en_ZA |
| dc.subject | Facies (Geology) | en_ZA |
| dc.subject | Granulite facies rocks -- South Africa -- Limpopo Belt | en_ZA |
| dc.subject | Metapelites | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | An investigation of archean and paleoproterozoic metamorphic processes in the Limpopo belt via detailed analysis of reaction textures in metapelites from the Bandelierkop Formation, Southern Marginal Zone of the Limpopo belt | en_ZA |
| dc.type | Thesis | en_ZA |