Abstract:
Neoarchean granitoids are commonly exposed along Archean high-grade metamorphic
terranes, where they occur as granitoid gneisses. A number of issues, including the effect of
overprint event(s), can complicate the characterization of these granitoids in Archean
terranes. A case study is presented here highlighting the complexity of characterizing
Neoarchean granitoid magmatism from the Limpopo Complex high-grade terrane in
southern Africa. Neoarchean granitoids occurring within the Central Zone of the Limpopo
Complex include the ~2.73-2.64 Ga biotite±amphibole-bearing Alldays granitoid, the ~2.68-
2.62 Ga garnet-bearing Singelele leucogranite, the ~2.65-2.63 Ga Avoca granitoid with
pyroxene-bearing and pyroxene-absent variants, the ~2.65-2.62 Ga biotite-bearing Verbaard
granitoid and the ~2.61-2.58 Ga Bulai granitoid with pyroxene-bearing and pyroxene-absent
variants. Of the different granitoids, the Singelele leucogranite and Verbaard granitoid
exhibit evidence for anatectic overprint. This study focuses on characterizing the nature of
overprint in the Verbaard granitoid. Exposures in the Verbaard area show a conspicuous
network of garnet-bearing leucocratic veins overprinting the light greyish biotite-bearing
Verbaard granitoid. These leucocratic veins, with more or less straight line outline, do not
have any biotite-bearing melanocratic margins, indicating that they formed elsewhere. On
the other hand, the garnet-bearing irregular outline leucosomes associated with surrounding
metapelites have biotite-bearing melanocratic margins indicating in situ formation by partial
melting. Detailed mineral chemical characteristics of garnet occurring in the metapelite,
associated leucosome, and the Verbaard granitoid, indicate comparable composition,
Abstract vii
suggesting common origin. It is argued that the garnet in leucocratic veins overprinting the
Verbaard granitoid represent relics from the metapelites, with the leucocratic veins
representing segregated melt away from the source region. Of the two types of metapelites
found in the study area – high-Al and low-Al metapelites – the distinction between the two is
suggested as an artifact of the extent of partial melting, with the high-Al metapelite
preserving more of the restitic domains, while the low-Al metapelite preserving more of the
leucosomic material. Using rim-core-rim garnet mineral chemical profiles, the leucosomes
are suggested as sites of preservation of different stages of garnet formation in the
associated metapelites.
Whole-rock geochemical characteristics of carefully sampled garnet-free domains of the
Verbaard granitoid indicate that they are similar to low-HREE Archean TTGs. Comparison
with experimental melts from a variety of source rocks indicates that the Verbaard granitoid
was likely derived from the melting of metabasalts. A comparative exercise with other
Neoarchean granitoids from the Central Zone indicates that the compositional
characteristics of the Verbaard granitoid are closely comparable to those of the Alldays
granitoid. It is suggested that the Verbaard granitoid represents the manifestation of the
Alldays granitoid magmatism in the Verbaard area.
Otladisang, B (2024). Provenance of Garnet in the neoarchaen verbaard granitoid gneiss:complexity of characterizing granitoids in high-grade terranes. Afribary. Retrieved from https://afribary.com/works/provenance-of-garnet-in-the-neoarchaen-verbaard-granitoid-gneiss-complexity-of-characterizing-granitoids-in-high-grade-terranes
Otladisang, Basupi "Provenance of Garnet in the neoarchaen verbaard granitoid gneiss:complexity of characterizing granitoids in high-grade terranes" Afribary. Afribary, 12 Apr. 2024, https://afribary.com/works/provenance-of-garnet-in-the-neoarchaen-verbaard-granitoid-gneiss-complexity-of-characterizing-granitoids-in-high-grade-terranes. Accessed 07 Sep. 2024.
Otladisang, Basupi . "Provenance of Garnet in the neoarchaen verbaard granitoid gneiss:complexity of characterizing granitoids in high-grade terranes". Afribary, Afribary, 12 Apr. 2024. Web. 07 Sep. 2024. < https://afribary.com/works/provenance-of-garnet-in-the-neoarchaen-verbaard-granitoid-gneiss-complexity-of-characterizing-granitoids-in-high-grade-terranes >.
Otladisang, Basupi . "Provenance of Garnet in the neoarchaen verbaard granitoid gneiss:complexity of characterizing granitoids in high-grade terranes" Afribary (2024). Accessed September 07, 2024. https://afribary.com/works/provenance-of-garnet-in-the-neoarchaen-verbaard-granitoid-gneiss-complexity-of-characterizing-granitoids-in-high-grade-terranes