Article (Scientific journals)
Petrogenesis of Archean PGM-bearing chromitites and associated ultramafic-mafic-anorthositic rocks from the Guelb el Azib layered complex (West African craton, Mauritania)
Berger, J.; Diot, H.; Lo, K. et al.
2013In Precambrian Research, 224, p. 612-628
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Keywords :
Anorthosite; Archean tholeiite; Granulites; Layered complex; Mafic-ultramafic rocks; Archean; Mauritania; West African Craton
Abstract :
[en] The Archean Guelb el Azib layered complex (GAC) in the West African craton of Mauritania is composed of an association of serpentinites, chromitites, amphibolites and anorthosites with few fine-grained amphibolite dykes. The complex forms tectonic slices in 2.9-3.5. Ga TTG gneiss terrains in close association with supracrustal rocks (BIFs, impure marbles, amphibolites). It was affected by a main granulite-facies grade metamorphism (up to 900. °C at 5-6. kbar) with subsequent retrogression in amphibolite and greenschist facies conditions. The preserved igneous macrostructures, the mineral compositions and the nature of relic magmatic assemblages have been used to constrain the composition of the parental melts and the conditions of crystallization. According to petrological observations and to comparison with experimental data, the formation of the complex can be explained by fractionation of a slightly hydrous high-alumina basaltic melt at low pressure. The early fractionation of olivine and the absence of massive clinopyroxene fractionation before plagioclase saturation led to crystallization of highly calcic plagioclase with Fe-, Al-rich but Cr-poor chromite from a hydrous tholeiitic parental magma, similar to worldwide Archean tholeiites. The complex shares many similarities with Archean anorthosite layered complexes, possibly formed in a supra-subduction zone environment according to results obtained on similar 2.9-3.0. Ga complexes from Greenland and India (namely Fiskenaesset and Sittampundi). Three phases of PGE mineralization affected the GAC chromitites: (i) igneous crystallization of laurite; (ii) formation of late magmatic IPGE sulpho-arsenides (irarsite-hollingworthite) and (iii) hydrothermal Pt-Pd mineralization represented by sperrylite and rustenburgite. © 2012 Elsevier B.V.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Berger, J.;  Département des Sciences de la Terre et de l'Environnement, FRS-FNRS, Université Libre de Bruxelles, Belgium
Diot, H.;  UMR CNRS 6112, Laboratoire de Planétologie et de Géodynamique de Nantes, Université de Nantes, France
Lo, K.;  Université de Nouakchott, Mauritania
Ohnenstetter, D.;  Centre de Recherches Pétrographiques et Géochimiques, CNRS, F-54501 Vandoeuvre lès Nancy, France
Féménias, O.;  IAMGOLD Corporation, West Africa, Mali
Pivin, M.;  Département des Sciences de la Terre et de l'Environnement, FRS-FNRS, Université Libre de Bruxelles, Belgium
Demaiffe, D.;  Département des Sciences de la Terre et de l'Environnement, FRS-FNRS, Université Libre de Bruxelles, Belgium
Bernard, A.;  Département des Sciences de la Terre et de l'Environnement, FRS-FNRS, Université Libre de Bruxelles, Belgium
Charlier, Bernard  ;  Université de Liège - ULiège > Département de géologie > Pétrologie, géochimie endogènes et pétrophysique
Language :
English
Title :
Petrogenesis of Archean PGM-bearing chromitites and associated ultramafic-mafic-anorthositic rocks from the Guelb el Azib layered complex (West African craton, Mauritania)
Publication date :
2013
Journal title :
Precambrian Research
ISSN :
0301-9268
Publisher :
Elsevier, Netherlands
Volume :
224
Pages :
612-628
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 12 November 2014

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