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Differentiation of tholeiitic basalt to A-type granite in the Sept Iles layered intrusion, Canada

Namur Olivier, Charlier Bernard, Toplis Michael J., Higgins Michael D., Hounsell Véronique, Liégeois Jean-Paul et Vander Auwera Jacqueline. (2011). Differentiation of tholeiitic basalt to A-type granite in the Sept Iles layered intrusion, Canada. Journal of Petrology, 52, (3), p. 487-539.

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URL officielle: http://dx.doi.org/doi:10.1093/petrology/egq088

Résumé

The undeformed 564 Ma Sept Iles layered intrusion (Quebec, Canada) is a large igneous body of c. 20 000 km3. From the base to the top, it consists of a Layered Series dominated by troctolite and gabbro, an anorthositic Upper Border Series and a dominantly granitic Upper Series. The parent magma of the Layered Series is inferred to be an iron-rich tholeiitic basalt (48 wt % SiO2; 15 wt % FeOt). Whole-rock compositions from the chilled margin, dykes cross-cutting the Layered Series and silicic rocks from the Upper Series display continuous major and trace element geochemical trends ranging from basalts to ferroan metaluminous A-type granites (77 wt % SiO2). Initial 143Nd/144Nd (0·51201–0·51207) and 87Sr/86Sr (0·70353–0·70548) indicate a juvenile-mantle source and minimal contamination by old crust (1–2%) during crystallization. Geochemical modeling, using the MELTS thermodynamic calculator combined with equations predicting mineral–melt equilibria from experiments on tholeiitic basalts, indicate that basaltic to monzonitic melt compositions are in equilibrium with the troctolites and gabbros of the Layered Series. Fe–Ti oxides saturate early in the Layered Series, after 14% fractionation of plagioclase–olivine cumulates. Further fractionation of Fe–Ti oxide-bearing gabbros drives the residual liquids toward silica enrichment and iron depletion. Major and trace element modeling indicates that the A-type granites from the Upper Series were produced by protracted fractional crystallization of an iron-rich basaltic parent magma, at a fraction of residual liquid of only 8%. The observed relative volumes of mafic cumulates and silicic rocks in the intrusion are in agreement with the calculations. Most of the intermediate compositions correspond to magmatic mafic enclave-bearing granitoids and display geochemical evidence of hybridization. Intermediate compositions produced by fractional crystallization are scarce and a Daly gap occurs from 57 to 67 wt % SiO2. This gap could result either from the fractional crystallization process or from silicate–liquid immiscibility during that compositional interval.

Type de document:Article publié dans une revue avec comité d'évaluation
Volume:52
Numéro:3
Pages:p. 487-539
Version évaluée par les pairs:Oui
Date:Mars 2011
Sujets:Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Mots-clés:liquid line of descent, fractional crystallization, tholeiitic magma, MELTS, least-squares modeling, ferroan (A-type) granitoid, layered intrusion, ligne liquide de descente, cristallisation fractionnée, magma tholéiitique, modélisation des moindres carrés, granitoïde ferroan (type A), intrusion stratifiée
Déposé le:17 juill. 2018 18:24
Dernière modification:17 juill. 2018 18:24
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