- Title
- Geological, petrological and geochemical investigation of the c. 3.45 Ga Stolzburg TTG Pluton at Crushers’ Quarry, Barberton greenstone belt, South Africa
- Creator
- Mofammere, Thato Constance
- Subject
- Geology Barberton Greenstone Belt (Eswatini and South Africa)
- Subject
- Petrology Barberton Greenstone Belt (Eswatini and South Africa)
- Subject
- Geochemistry Barberton Greenstone Belt (Eswatini and South Africa)
- Subject
- Intrusions (Geology) Barberton Greenstone Belt (Eswatini and South Africa)
- Subject
- Tonalite-Trondhjemite-Granodiorite
- Date Issued
- 2025-04-02
- Date
- 2025-04-02
- Type
- Academic theses
- Type
- Master's theses
- Type
- text
- Identifier
- http://hdl.handle.net/10962/479163
- Identifier
- vital:78266
- Description
- This study investigates the tonalite-trondhjemite-granodiorite (TTG) suite and associated amphibolite xenoliths of the Stolzburg pluton at Crushers’ Quarry in the Barberton Granitoid-Greenstone Terrain, South Africa. Through detailed field mapping, petrography, geochemical analysis, δ¹⁸O investigation of quartz, and U-Pb zircon geochronology, the petrogenesis and geodynamic context of these Archean rocks were explored. Five major lithologies were identified: Coarse-grained trondhjemites, medium-grained tonalites, fine-grained tonalites, granodiorite sheets, and amphibolite xenoliths. Field evidence, including cross-cutting relationships, indicates that the coarse-grained trondhjemites intruded as the earliest phase, followed by medium-grained tonalites, which were then followed by fine-grained tonalites, and finally, granodiorite sheets, which represent the latest intrusive phase. Petrographic analysis reveals mineralogical differences between the trondhjemites and tonalites, with trondhjemites lacking hornblende and having lower mafic mineral content. Geochemical data support the interpretation that the TTGs formed through partial melting of variably hydrated metabasaltic sources (possibly at depth in the garnet stability field). The metabasaltic melt incorporated varying proportions of older, intermediate trondhjemite crust and volcaniclastic sediments during ascent and emplacement to form the Stolzburg pluton TTG suite of rocks. Elevated (above mantle) δ¹⁸O quartz values of the Stolzburg pluton TTG rocks ranging between 8.72 to 9.71‰ combined with it’s strongly peraluminous geochemical composition indicate the presence of an ancient crustal component that was assimilated into the metabasaltic melt source(s). It is proposed that a number of petrogenetic factors controlled the composition of the Stolzburg TTG rocks, including composition of the metabasalt source, degree of hydration of the metabasalt source and the extent of crustal contamination with older, pre-existing intermediate composition rocks. A possible candidate for the crustal contamination component could be the older 3.509 Ga Steynsdorp trondhjemite as well as ancient volcaniclastic sediments in the greenstone belt. The protolith to the amphibolite xenoliths occurring within the TTG suite are geochemically characterized as komatiitic basalt, recording either a subduction zone or crustal contamination geochemical signature. U-Pb zircon dating of the coarse-grained trondhjemites and medium-grained tonalites yield Concordia ages of 3429.9 ± 12 Ma (2σ) and 3414.0 ± 14 Ma (2σ), respectively. These Concordia ages represent an estimate of the igneous crystallization ages of the zircons and confirm that these TTGs were emplaced in close temporal succession. The U-Pb zircon ages are comparable to those in the published literature, although one sample with a significantly younger age is attributed to zircon open-system Pb-loss in complex early Archean zircons and also challenges with the LA-ICP-MS analytical technique used. The depth of metabasalt melting is not constrained in this study, similar to recent studies on early Archean TTGs. Various TTG geodynamic settings are explored ranging from melting at the base of a thick oceanic plateau to generation at depth in a subduction zone. In light of recent regional field observations, metamorphic constraints, apatite thermochronological data, U-Pb detrital zircon data and greenstone belt metabasalt geochemistry, a model of TTG crust generation in an episodic proto-subduction zone, involving subcretion and tectonic imbrication of oceanic lithosphere at c. 3.45 Ga, is considered.
- Description
- Thesis (MSc) -- Faculty of Science, Geology, 2025
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (137 pages)
- Format
- Publisher
- Rhodes University
- Publisher
- Faculty of Science, Geology
- Language
- English
- Rights
- Mofammere, Thato Constance
- Rights
- Use of this resource is governed by the terms and conditions of the Creative Commons "Attribution-NonCommercial-ShareAlike" License (http://creativecommons.org/licenses/by-nc-sa/2.0/)
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| Thumbnail | File | Description | Size | Format | |||
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