Hafnium-Neodymium isotope, trace element and U-Pb zircon age constraints on the petrogenesis of the 3.44-3.46 Ga Dwalile greenstone remnant, Ancient gneiss Complex, Swaziland

Hoffmann, J. Elis; Musese, Emmanuel; Kroener, Alfred; Schneider, Kathrin P.; Wong, Jean; Hofmann, Axel; Hegner, Ernst; Kasper, Haino Uwe; Tusch, Jonas and Muenker, Carsten (2020): Hafnium-Neodymium isotope, trace element and U-Pb zircon age constraints on the petrogenesis of the 3.44-3.46 Ga Dwalile greenstone remnant, Ancient gneiss Complex, Swaziland. In: Precambrian Research, Vol. 351, 105970

Abstract

The geodynamic setting of the 3.44-3.46 Ga Dwalile greenstone remnant (DGR) of the Ancient Gneiss Complex (Swaziland) and its relationship to other Greenstone belts of similar age is investigated in this contribution. We present Hf-Nd isotope, major and trace element data for komatiites, komatiitic basalts, basalts, basaltic andesites as well as felsic volcanic and sedimentary rocks, all metamorphosed at amphibolite-facies grade. Major and trace element compositions of metabasalts and metakomatiites indicate crustal contamination. The best-preserved samples yield Lu-176-Hf-176 and Sm-147-Nd-143 isochron ages of ca. 3500 and 3460 Ma, respectively, in line with U-Pb zircon ages of interlayered felsic volcanic rocks of 3460 Ma. Isotope and trace element data for the metasedimentary rocks reveal a contribution of older crustal material with 3.53 Ga zircon grains. Together with >3.7 Ga inherited zircon grains in the Ngwane gneiss (NG) of the basement, this evidence supports a model of deposition of the Dwalile supracrustal rocks on or near older continental crust. Initial epsilon Hf and epsilon Nd values of the least contaminated DGR metabasalts and metakomatiites are similar to those of the contemporaneous Komati Formation komatiites and tholeiitic basalts, however, the trace element composition and slight correlations of initial epsilon Hf and epsilon Nd values with major and trace element parameters indicative for crustal contamination reveal differences in the basement of both units.

• Item Type: Journal article
• Faculties: Geosciences > Department of Earth and Environmental Sciences
• Subjects: 500 Science > 550 Earth sciences and geology
• ISSN: 0301-9268
• Language: English