Universität zu Köln

Viehmann, Sebastian ORCID: 0000-0001-6138-5862, Hoffmann, J. Elis ORCID: 0000-0001-6670-1393, Muenker, Carsten and Bau, Michael (2014). Decoupled Hf-Nd isotopes in Neoarchean seawater reveal weathering of emerged continents. Geology, 42 (2). S. 115 - 119. BOULDER: GEOLOGICAL SOC AMER, INC. ISSN 1943-2682

Full text not available from this repository.

Abstract

Marine chemical sediments from the Temagami banded iron formation (BIF) in Canada exhibit nonchondritic Zr/Hf and Y/Ho ratios and seawater-like rare earth element patterns, indicating that their Hf and Nd are not detrital, but derived from seawater. This is confirmed by Sm-Nd and Lu-Hf isochron ages of 2605 +/- 140 Ma (initial epsilon(Nd) +0.03 +/- 4.1) and 2760 +/- 120 Ma (initial epsilon(Hf) +/- 7.2 +/- 5.3), respectively, that overlap within error the 2.7 Ga U-Pb age of associated igneous rocks. The Temagami BIF is therefore an excellent archive of the Nd-Hf isotopic composition of Neoarchean seawater. Whereas epsilon(Nd2.7Ga) values cluster around +1, epsilon(Hf2.7Ga) values range from +6.7 to +24.1, substantially more radiogenic than those of ambient Neoarchean mantle and continental crust. Such an epsilon(Hf)-epsilon(Nd) distribution is typical of modern seawater, plotting above the terrestrial array as defined by igneous and clastic sedimentary rocks. The only mechanism known to produce natural waters with decoupled Nd and Hf isotope compositions is the incongruent mobilization of Hf from continental crustal material. Therefore, input of such highly radiogenic Hf into seawater requires substantial amounts of evolved Neoarchean continental crust that was exposed above sea level and available to erosion and terrestrial weathering.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Viehmann, Sebastian UNSPECIFIED orcid.org/0000-0001-6138-5862 UNSPECIFIED Hoffmann, J. Elis UNSPECIFIED orcid.org/0000-0001-6670-1393 UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED Bau, Michael UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-446293
DOI:	10.1130/G35014.1
Journal or Publication Title:	Geology
Volume:	42
Number:	2
Page Range:	S. 115 - 119
Date:	2014
Publisher:	GEOLOGICAL SOC AMER, INC
Place of Publication:	BOULDER
ISSN:	1943-2682
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language RARE-EARTH-ELEMENT; IRON-FORMATIONS; FERROMANGANESE NODULES; SEDIMENTARY SYSTEM; NEODYMIUM ISOTOPES; GREENSTONE-BELT; SOUTH-AFRICA; HAFNIUM; EVOLUTION; CRUSTS Multiple languages Geology Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/44629