Generation of early Archaean felsic greenstone volcanic rocks through crustal melting in the Kaapvaal, craton, southern Africa

• Published in: Earth and planetary science letters Vol. 381; pp. 188 - 197
• Main Authors: Kröner, Alfred, Elis Hoffmann, J., Xie, Hangqiang, Wu, Fuyuan, Münker, Carsten, Hegner, Ernst, Wong, Jean, Wan, Yusheng, Liu, Dunyi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2013
• Subjects: Barberton Greenstone Belt; Cratons; Crusts; Decapoda; Formations; greenstone evolution; Komatiites; Marine; Melting; Nd–Hf isotopes; Precursors; Rocks; Zircon; zircon age; Barberton Greenstone Belt; Nd–Hf isotopes; zircon age; greenstone evolution
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2013.08.029

High-potassium felsic volcanic rocks interlayered with basalt and komatiite in early Archaean greenstone sequences in the Barberton Greenstone Belt of South Africa and Swaziland, previously considered to be derived from melting of mafic precursors, are shown to be the result of melting of significantly older felsic crust. This is documented by a combination of SHRIMP zircon dating with Hf-in-zircon and whole-rock Lu–Hf and Sm–Nd isotopic data. Zircons from felsic rocks of the oldest Barberton unit, the 3.53 Ga Theespruit Formation, yielded predominantly negative εHf(t)-values, whereas whole-rock εHf(t)- and εNd(t)-data are slightly negative to slightly positive. Similar results were obtained for ca. 3.45 Ga felsic rocks in the Hoeggenoog and Noisy Formations higher up in the greenstone stratigraphy. These data rule out derivation of the felsic units from melting of basaltic precursors and favor a crustal source, most likely of TTG composition. The isotopic data are not compatible with an entirely oceanic origin of the Barberton greenstone sequences and favor a pre-greenstone basement beneath the volcanic rocks. Crustal melting of Eo- to Paleoarchaean lower crust probably generated the felsic volcanic rocks and is likely to have been responsible for gradual stabilization of the Kaapvaal craton. •Barberton Greenstone Belt felsic volcanics resulted from melting of older crust.•Hf and Nd isotopic data yieded predominantly negative εHf(t)- and εNd(t)-values.•An entirely intra-oceanic evolution of the greenstone belt is unlikely.•Early Archaean intracrustal melting has contributed towards cratonization.