کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4723366 1639650 2013 17 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Petrogenesis of Archean PGM-bearing chromitites and associated ultramafic–mafic–anorthositic rocks from the Guelb el Azib layered complex (West African craton, Mauritania)
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
Petrogenesis of Archean PGM-bearing chromitites and associated ultramafic–mafic–anorthositic rocks from the Guelb el Azib layered complex (West African craton, Mauritania)
چکیده انگلیسی

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.


► New petrological data on an Archean anorthosite complex in the West African craton.
► Formed by the low pressure fractional crystallization of hydrous high-Al basalt.
► Evolved Archean tholeiite magma crystallized Fe-rich chromites and anorthosites.
► Three phases of PGE mineralization: igneous, late-magmatic and hydrothermal.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Precambrian Research - Volume 224, January 2013, Pages 612–628
نویسندگان
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