Universität zu Köln

Schneider, Kathrin P., Hoffmann, J. Elis ORCID: 0000-0001-6670-1393, Boyet, Maud, Muenker, Carsten and Kroener, Alfred (2018). Coexistence of enriched and modern-like Nd-142 signatures in Archean igneous rocks of the eastern Kaapvaal Craton, southern Africa. Earth Planet. Sci. Lett., 487. S. 54 - 67. AMSTERDAM: ELSEVIER SCIENCE BV. ISSN 1385-013X

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Abstract

The short-lived Sm-146-Nd-142 isotope system is an important tool for tracing Hadean crust-mantle differentiation processes and constraining their imprint on much younger rocks from Archean cratons. We report the first comprehensive set of high-precision Nd-142 analyses for granitoids and amphibolites of the Ancient Gneiss Complex (AGC; Swaziland) and the oldest metavolcanic units of the Barberton Greenstone Belt (BGB; South Africa). The investigated samples span an age range from 3.66 Ga to 3.22 Ga and are representative of major geological units of the AGC and the lower Onverwacht Group of the BGB. Measured samples yielded 1.0 42 Nd values in the range from -8 ppm to +3 ppm relative to the JNdi-1 terrestrial standard, with typical errors smaller than 4.4 ppm. The distribution of the p(142)Nd values for these 17 measured samples is bimodal with ten samples showing a tendency towards slightly negative mu Nd-142 anomalies, whereas seven samples have Nd-142 similar to the terrestrial reference. The only confidently resolvable mu Nd-142 anomalies were found in a 3.44 Ga Ngwane Gneiss sample and in amphibolites of the ca. 3.45 Ga Dwalile Greenstone Remnant, revealing 1.1 142 Nd values ranging from -7.9 +/- 4.4 to -6.1 +/- 4.3 ppm. The mu Nd-142 deficits do not correlate with age, lithological unit, or sample locality. Instead, our results reveal that two distinct mantle domains were involved in the formation of the AGC crust. The two reservoirs can be distinguished by their mu Nd-142 signatures. Mantle-derived rocks tapped the enriched reservoir with negative mu Nd-142 at least until 3.46 Ga, whereas the granitoids preserved a negative mu Nd-142 signature that formed by incorporation of older AGC crust at least until 3.22 Ga. The oldest gneisses with no mu Nd-142 anomaly are up to 3.64 Ga in age, indicating that a modern terrestrial Nd-142 reservoir was already present by early Archean times. (C) 2018 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Schneider, Kathrin P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hoffmann, J. Elis UNSPECIFIED orcid.org/0000-0001-6670-1393 UNSPECIFIED Boyet, Maud UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED Kroener, Alfred UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-191096
DOI:	10.1016/j.epsl.2018.01.022
Journal or Publication Title:	Earth Planet. Sci. Lett.
Volume:	487
Page Range:	S. 54 - 67
Date:	2018
Publisher:	ELSEVIER SCIENCE BV
Place of Publication:	AMSTERDAM
ISSN:	1385-013X
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language BARBERTON GREENSTONE-BELT; ANCIENT GNEISS COMPLEX; HADEAN MAFIC CRUST; GRANITIC-ROCKS; EARTHS MANTLE; ISOTOPE SYSTEMATICS; CONTINENTAL-CRUST; KOMATIITES; EVOLUTION; HF Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/19109