Characterisation of early Archaean chemical sediments by trace element signatures

Bolhar, R, Kamber, BS, Moorbath, S, Fedo, CM and Whitehouse, MJ (2004) Characterisation of early Archaean chemical sediments by trace element signatures. Earth And Planetary Science Letters, 222 1: 43-60. doi:10.1016/j.epsl.2004.02.016


Author Bolhar, R
Kamber, BS
Moorbath, S
Fedo, CM
Whitehouse, MJ
Title Characterisation of early Archaean chemical sediments by trace element signatures
Journal name Earth And Planetary Science Letters   Check publisher's open access policy
ISSN 0012-821X
Publication date 2004
Sub-type Article (original research)
DOI 10.1016/j.epsl.2004.02.016
Volume 222
Issue 1
Start page 43
End page 60
Total pages 18
Editor Dr E. Boyle
E. Bard
Place of publication Netherlands
Publisher Elsevier Science BV
Collection year 2004
Language eng
Subject C1
260304 Inorganic Geochemistry not elsewhere classified
Abstract Rare earth element (REE) plus yttrium (Y) patterns of modem seawater have characteristic features that can be used as chemical fingerprints. Reliable proxies for marine REE + Y chemistry have been demonstrated from a large geological time span, including Archaean banded iron formation (BIF), stromatolitic limestone, Phanerozoic reef carbonate and Holocene microbialite. Here we present new REE + Y data for two distinct suites of early Archaean (ca. 3.7-3.8 Ga) metamorphosed rocks from southern West Greenland, whose interrelationships, if any, have been much debated in recent literature. The first suite comprises mangetite-quartz BIF, magnetite-carbonate BIF and banded magnetite-rich quartz rock, mostly from the Isua Greenstone Belt (IGB). The REE + Y patterns, particularly diagnostic anomalies (Ce/Ce*, Pr/Pr*), are closely related to those of published seawater proxies. The second suite includes banded quartz-pyroxene-amphibole +/- garnet rocks with minor magnetite from the so-called Akilia Association enclaves (in early Archaean granitoid gneisses) of the coastal region, some 150 km southwest of the IGB. Rocks of this type from one much publicised and highly debated locality (the island of Akilia) have been identified by some workers [Nature 384 (1996) 55; Geochim. Cosmochim. Acta 61 (1997) 2475] as BIF-facies, and their C-13-depleted signature in trace graphite interpreted as a proxy for earliest life on Earth. However, REE + Y patterns of the Akilia Association suite (except for one probably genuine magnetite-rich BIF from Ugpik) are inconsistent with a seawater origin. We agree with published geological and geochemical (including REE) work [Science 296 (2002) 1448] that most of the analysed Akilia rocks are not chemical sediments, and that C-isotopes in such rocks therefore cannot be used as biological proxies. Application of the REE + Y discriminant for the above two rock suites has been facilitated in this study by the use of MC-ICP technique which yields a more complete and precise REE + Y spectrum than was available in many previous studies. (C) 2004 Elsevier B.V. All rights reserved.
Keyword Geochemistry & Geophysics
Archaean
Banded Iron Formation
Isua Greenstone Belt
Chemical Sediments
Metasomatism
Ree Plus Y
Seawater Composition
Rare-earth-elements
Banded Iron-formations
Southern West Greenland
Isua Supracrustal Belt
Field Evidence
Ce Oxidation
3.8-3.7 Ga
Icp-ms
Seawater
Yttrium
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Earth Sciences Publications
2005 Higher Education Research Data Collection
 
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Created: Wed, 15 Aug 2007, 04:44:44 EST