Universität zu Köln

Kroener, Alfred, Hoffmann, J. Elis ORCID: 0000-0001-6670-1393, Xie, Hangqiang, Munker, Carsten ORCID: 0000-0001-6406-559X, Hegner, Ernst, Wan, Yusheng, Hofmann, Axel ORCID: 0000-0002-8801-0443, Liu, Dunyi and Yang, Jinhui (2014). Generation of early Archaean grey gneisses through melting of older crust in the eastern Kaapvaal craton, southern Africa. Precambrian Res., 255. S. 823 - 847. AMSTERDAM: ELSEVIER. ISSN 1872-7433

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Abstract

We report zircon ages, Hf-in-zircon isotopes as well as whole-rock geochemistry and Hf-Nd isotopic systematics for Palaeoarchaean grey gneisses of the Ancient Gneiss Complex of Swaziland, the oldest components of the Kaapvaal craton, southern Africa. The Hf-in-zircon isotopic compositions in these compositionally heterogeneous, multicomponent, migmatitic gneisses are highly variable, even in the oldest zircons dating back to 3.66 Ga, suggesting growth of zircon from melts representing a mix of juvenile and anatectic material derived from differentiated continental crust of Eoarchean to late Hadean age. In contrast, the initial Nd and Hf whole-rock isotopic compositions are frequently not in agreement with the Hf-in-zircon data that mostly show approximately chondritic initial values for Nd and strongly radiogenic initial values for Hf. We consider it likely that both the Lu-Hf and Sm-Nd whole-rock isotopic systems were disturbed and partly reset during later episodes of partial melting and crustal reworking, most likely during a pervasive 3.2 Ga tectono-metamorphic event. Primitive mantle-normalized trace element patterns show the variable influence of residual plagioclase and garnet in the sources as well as high contents of strongly incompatible elements. In conjunction with the Hf-in-zircon isotopic data the trace element contents are best explained by the incorporation of older continental crustal material into the sources of the grey gneisses. Our data support evidence from other Palaeoarchean terranes that crustal recycling, as seen in even the oldest crustal components, played an important role in early continental evolution. Rocks previously classified as a subduction-related tonalite-trondhjemite-granodiorite suite are complex, and their chemistry alone cannot be used to reconstruct tectonic settings. (C) 2014 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Kroener, Alfred UNSPECIFIED UNSPECIFIED UNSPECIFIED Hoffmann, J. Elis UNSPECIFIED orcid.org/0000-0001-6670-1393 UNSPECIFIED Xie, Hangqiang UNSPECIFIED UNSPECIFIED UNSPECIFIED Munker, Carsten UNSPECIFIED orcid.org/0000-0001-6406-559X UNSPECIFIED Hegner, Ernst UNSPECIFIED UNSPECIFIED UNSPECIFIED Wan, Yusheng UNSPECIFIED UNSPECIFIED UNSPECIFIED Hofmann, Axel UNSPECIFIED orcid.org/0000-0002-8801-0443 UNSPECIFIED Liu, Dunyi UNSPECIFIED UNSPECIFIED UNSPECIFIED Yang, Jinhui UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-421080
DOI:	10.1016/j.precamres.2014.07.017
Journal or Publication Title:	Precambrian Res.
Volume:	255
Page Range:	S. 823 - 847
Date:	2014
Publisher:	ELSEVIER
Place of Publication:	AMSTERDAM
ISSN:	1872-7433
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language BARBERTON GREENSTONE-BELT; TRONDHJEMITE-GRANODIORITE TTG; HAFNIUM ISOTOPE EVIDENCE; LU-HF; U-PB; CONTINENTAL-CRUST; NORTHWESTERN CANADA; GRANITIC-ROCKS; TONALITIC GNEISS; WYOMING PROVINCE Multiple languages Geosciences, Multidisciplinary Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/42108