Universität zu Köln

Schneider, K. P., Hoffmann, J. E., Muenker, C., Patyniak, M., Sprung, P., Roerdink, D., Garbe-Schoenberg, D. and Kroener, A. (2019). Petrogenetic evolution of metabasalts and metakomatiites of the lower Onverwacht Group, Barberton Greenstone Belt (South Africa). Chem. Geol., 511. S. 152 - 178. AMSTERDAM: ELSEVIER SCIENCE BV. ISSN 1872-6836

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Abstract

A well-preserved sequence, by Archean standards, of mantle-derived metabasalts and metakomatiites forms large parts of the lower Onverwacht Group of the Barberton Greenstone Belt (South Africa). To elucidate the origin of mafic and ultramafic rocks from this 3.55 to 3.45 Ga sequence, we present a comprehensive geochemical dataset including major and trace elements as well as Lu-Hf and Sm-Nd isotope compositions for a variety of metavolcanic rocks. These include metabasalts of the amphibolite-facies Sandspruit and Theespruit Formations as well as metabasalts and metakomatiites of the lower greenschist-facies Komati Formation. Based on their incompatible trace element patterns, the basalts of the Sandspruit and Theespruit Formations can be subdivided into a light rare earth element (LREE) depleted group, a LREE-undepleted group, and a LREE-enriched group. Positive epsilon Hf-(t) and epsilon Nd-(t) values of ca. +3 to +4 and 0 to +2, respectively, together with depletions in Th and La-CN/Yb-CN indicate derivation of the LREE-depleted basalts from a depleted mantle source. However, chondritic epsilon Hf-(t) and epsilon Nd-(t) values combined with positive Th and La-CN/Yb-CN of the LREE-enriched samples indicate a contribution from older granitoid crust in the petrogenesis of these samples. Trace element patterns of komatiites and basalts of the Komati Formation are generally flat relative to primitive mantle with slight depletions in heavy rare earth elements and Th and overall positive epsilon Hf-(t) of + 2.5 +/- 3.5 (2 s.d.) and epsilon Nd-(t) of + 0.5 +/- 2.2 (2 s. d.). The coherence in trace element characteristics suggests a common magmatic origin for basalts and komatiites. This study reveals that the two lavas were derived from the same mantle plume, i. e. komatiites were formed by high degrees of melting of a depleted mantle source containing residual garnet and the basalts were formed by moderate degrees of partial melting in shallower regions of the mantle. Based on the current dataset, combined with published data, we propose a geodynamic model for the oldest units of the Barberton Greenstone Belt that describes the development from a submerged continental setting (for the Sandspruit and Theespruit Formations) to a submarine plateau setting (for the Komati Formation) as a consequence of continental rifting.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Schneider, K. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hoffmann, J. E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Patyniak, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Sprung, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Roerdink, D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Garbe-Schoenberg, D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kroener, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-150519
DOI:	10.1016/j.chemgeo.2019.02.020
Journal or Publication Title:	Chem. Geol.
Volume:	511
Page Range:	S. 152 - 178
Date:	2019
Publisher:	ELSEVIER SCIENCE BV
Place of Publication:	AMSTERDAM
ISSN:	1872-6836
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language ARCHEAN CONTINENTAL-CRUST; EASTERN KAAPVAAL CRATON; HF GARNET GEOCHRONOLOGY; ND ISOTOPIC COMPOSITION; SM-ND; MOUNTAIN LAND; LU-HF; WEST GREENLAND; VOLCANIC-ROCKS; TRACE-ELEMENT Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/15051