Geochemistry of mafic-ultramafic rocks of the 3.33 Ga Kromberg type-section, Barberton greenstone belt, South Africa: Implications for early Earth geodynamic processes

0558659 - GLÚ 2023 RIV NL eng J - Článek v odborném periodiku
Grosch, E. G. - Ndlela, S. - Murphy, D. - McLoughlin, N. - Trubač, J. - Sláma, Jiří
Geochemistry of mafic-ultramafic rocks of the 3.33 Ga Kromberg type-section, Barberton greenstone belt, South Africa: Implications for early Earth geodynamic processes.
Chemical Geology. Roč. 605, September (2022), č. článku 120947. ISSN 0009-2541. E-ISSN 1872-6836
Institucionální podpora: RVO:67985831
Klíčová slova: Barberton greenstone belt * Archean metabasalts * Early Earth geodynamics
Obor OECD: Geology
Impakt faktor: 3.9, rok: 2022
Způsob publikování: Omezený přístup
https://www.sciencedirect.com/science/article/pii/S0009254122002418?via%3Dihub

In conjunction with major, trace and rare earth element data, this study presents the first whole-rock Lu–Hf isotope analyses of mafic-ultramafic rocks of the c. 3.3 Ga Kromberg type-section in the Barberton greenstone belt of South Africa. Three compositionally distinct volcanic rock types are identified namely Group 1 metabasalts, Group 2 metabasalts and komatiitic metabasalts. Group 1 metabasalts are Fe–Mg tholeiitic with compositions that plot close to the Primitive Mantle composition, have isochron intercept εHf(t) value of 0.01 ± 0.4 and Eoarchean Hf model ages. Group 2 metabasalts have very high Al₂O₃/TiO₂ ratios (c. 50), small negative Nb anomalies, LREE-depleted slightly concave up REE patterns, and negative ε_Hf(t) values. The komatiitic basalts variably record small negative Nb anomalies in a primitive mantle normalized plot. Group 1 metabasalts and cumulate peridotites (wehrlites) yield a Lu–Hf isochron age of 3.340 ± 0.190 Ga (95% confidence level). The highly variable major and trace element geochemistry of the rocks in the sequence implies highly dynamic and variable mantle melting environments. The Group 2 metabasalts have geochemical characteristics similar to that of boninites and are interpreted to have formed from a shallow, refractory mantle source. Group 2 metabasalts are argued to have formed in a proto-plate tectonic back-arc basin involving crustal contamination, whereas Group 1 metabasalts likely formed from within a deep mantle plume.
Trvalý link: https://hdl.handle.net/11104/0333547