Garnet-bearing low-Sr and high-Sr Singelele leucogranite: A record of Neoarchean episodic melting in collisional setting and Paleoproterozoic overprint in the Beit Bridge complex, southern Africa

Journal article

Authors / Editors

Rajesh, Hariharan

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Publication Details

Author list: Rajesh HM, Belyanin GA, Safonov OG, Vorster C, Van Reenen DD

Publisher: Elsevier

Place: AMSTERDAM

Publication year: 2018

Journal: Lithos: Journal of Petrology, Mineralogy and Geochemistry (0024-4937)

Journal acronym: LITHOS

Volume number: 322

Start page: 67

End page: 86

Number of pages: 20

ISSN: 0024-4937

Languages: English-Great Britain (EN-GB)

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Abstract

The study presents field, petrographic, mineral chemical, bulk-rock geochemical, U-Pb zircon and Ar-40/Ar-39 amphibole-biotite geochronologic characteristics of the Singelele leucogranite, which constitutes a prominent Neoarchean magmatic event in the Beit Bridge Complex terrane of the Limpopo Complex, southern Africa. The Singelele leucogranite is magnesian to ferroan, calcic to alkalic and peraluminous. Two groups of granites are distinguished on the basis of bulk-rock Sr content and garnet chemistry: low-Sr with low-X-Mg garnet and high-Sr with high X-Mg garnet. Major and trace element characteristics show that these two groups were, probably, generated by a fluid-absent melting of crustal rocks like metagreywacke at different depths in collision tectonic setting. Spatial distribution and available geochronologic data indicate that these two groups represent two episodes of Singelele leucogranite magmatism: low-Sr at similar to 2.68-2.65 Ga and high-Sr at similar to 2.63-2.62 Ga. The Singelele leucogranite occurring close to major fold structures and faults/shear zones are locally affected by anatectic and metasomatic Paleoproterozoic overprint at similar to 2.0 Ga (2037 +/- 21 Ma and 2015 +/- 15 Ma U-Pb for zircon over-growths). Zoning of coarse garnet grains with a decrease of X-ca in the melting-overprinted rocks reflects decompression of about 3-4 kbar. The metasomatic overprint produces Cl-F-rich biotite-2 and amphibole. Phase equilibria modeling shows a lack of equilibrium between these minerals and earlier garnet, and indicates modification of the garnet composition by metasomatism. Ar-40/Ar-39 ages for amphibole (2043 +/- 18 Ma, 1994 +/- 12 Ma) and biotite-2 (1985 +/- 11 Ma, 1967 +/- 11 Ma) are consistent with the zircon overgrowth ages. (C) 2018 Elsevier B.V. All rights reserved.

Keywords

Anatectic and metasomatic overprint, Archean high-grade terrane, Fluid-absent melting, Garnet-bearing peraluminous leucogranite, Low-Sr and high-Sr leucogranite, Metagreywacke

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