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Origin of antecrysts in igneous rocks from the Salavat Range (NW Iran): an explanation for the geochemical signature of potassic alkaline rocks

soltanmohammadi Azam, Grégoire Michel, Ceuleneer Georges, Benoit Mathieu, Bédard L. Paul, Gouy Sophie et Rabinowicz Michel. (2021). Origin of antecrysts in igneous rocks from the Salavat Range (NW Iran): an explanation for the geochemical signature of potassic alkaline rocks. Journal of Petrology, 62, (7), egab031.

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URL officielle: http://dx.doi.org/doi:10.1093/petrology/egab031

Résumé

Abundant silica-undersaturated potassic lavas are found in the centre of the Turkish–Iranian plateau (NW Iran) as flows, pillows and dykes. They display abundant zoned clinopyroxene macrocrysts and xenoliths of igneous cumulates. We determined four types of zoned crystals (Type-I, -II, -III and -IV) on the basis of their composition and zoning patterns. Use of in situ compositional data, together with whole-rock major and trace elements and the isotopic signatures of the host lavas provided evidence for the derivation of the different types of zoned clinopyroxenes from at least two contrasting parental melts. Our findings are consistent with an origin of the ultrapotassic and sodic alkaline melts from the deep-seated compaction pockets inferred from our previous studies of the alkaline magmatism throughout the Turkish–Iranian plateau. The ultrapotassic melt, which accumulated at the top of the compaction pockets, eventually ponded close to the spinel–garnet mantle transition and generated colourless antecrysts (Type-I and Type-II) and clinopyroxenite cumulates. When the compaction pocket impinged on the continental lithosphere, interstitial melts segregated and flowed inside dykes where grass green antecrysts (Type-III) and zoned phenocrysts (Type-IVa) crystallized from a melt having a geochemical signature of sodic alkaline melt. Later, at the crustal level, melt crystallization processes produced Type-IVb zoned phenocrysts. Our results are at odds with the paradigm of potassic magmas in NW Iran being derived strictly from a single mantle source.

Type de document:Article publié dans une revue avec comité d'évaluation
Volume:62
Numéro:7
Pages:egab031
Version évaluée par les pairs:Oui
Date:Juillet 2021
Sujets:Sciences naturelles et génie > Génie
Sciences naturelles et génie > Sciences appliquées
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
Unités de recherche > Laboratoire des Matériaux Terrestres
Mots-clés:potassic alkaline rocks, zoned clinopyroxene, mixing, antecrysts, cumulates, Turkish–Iranian plateau, compaction pocket, roches alcalines potassiques, clinopyroxène zoné, mélange, antécristaux, cumulats, plateau turco-iranien, poche de compactage
Déposé le:21 déc. 2021 00:48
Dernière modification:21 déc. 2021 00:48
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