Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Archean High-Mg Quartz-Monzodiorite Suite : A Re-evaluation of the Parental Magma and Differentiation

Bédard L. Paul. (1996). Archean High-Mg Quartz-Monzodiorite Suite : A Re-evaluation of the Parental Magma and Differentiation. The Journal of Geology, 104, (6), p. 713-728.

[img] PDF - Version publiée
Administrateurs seulement

1MB

URL officielle: https://www.jstor.org/stable/30081163

Résumé

Quartz-monzodiorite is generally considered to represent the parent magma of high-Mg quartz-monzodiorite plutonic suites; thus such suites are thought to be melts from a metasomatized mantle wedge. It is proposed here that hornblende tonalite, which is present in the feeder dikes of high-Mg quartz-monzodiorite plutonic suites, better represents the parental magma. Hornblende tonalite has a higher compatible element content with a relatively lower incompatible element content and a lower (La/Yb)n ratio than quartz-monzodiorite, suggesting that the tonalite is the more primitive magma of the suite. The hornblendite unit of the high-Mg quartz-monzodiorite plutonic suite is interpreted to represent the cumulate, and the quartz-monzodiorite the differentiated liquid. To test this hypothesis and explain the differentiation of the units of a high-Mg quartz-monzodiorite plutonic suite, the Houghton pluton in the northern Abitibi greenstone belt, Quebec, was studied. Results show that crystal fractionation and equilibrium crystallization cannot sufficiently enrich incompatible elements in the quartz-monzodiorite while keeping the compatible element contents high. Feeder dike petrography suggests that the magma chamber was periodically replenished. The model that best explains the formation of the different units of this suite is a periodically replenished magma chamber with a crystallization sequence of hornblende followed by hornblende and plagioclase. Such a magma chamber undergoing crystal fractionation will produce the high incompatible and compatible element contents typical of quartz-monzodiorite magmas. Not all quartz-monzodiorite magmas of the site can be explained by a replenishment of the hornblende tonalite. As identified in the feeder system, the replenishing magma changed at some time to one represented by leucotonalite-to-quartz-diorite. By changing the replenishing magma from the hornblende tonalite to the leucotonalite-to-quartz-diorite unit, after the differentiated liquid reached 64% SiO2, it is possible to model all the units in the plutonic suite. The hornblendite unit can be easily modeled for the major oxides, but the inclusion or exclusion of accessory phases rich in trace elements (allanite) in the samples renders trace element behavior erratic, and the hornblendite cannot be successfully modeled.

Type de document:Article publié dans une revue avec comité d'évaluation
Volume:104
Numéro:6
Pages:p. 713-728
Version évaluée par les pairs:Oui
Date:Novembre 1996
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 > Module d'ingénierie
Unités de recherche > Laboratoire des Matériaux Terrestres
Mots-clés:Quartz-monzodiorite, magma, high-Mg, formation, haute teneur en Mg
Déposé le:15 mars 2022 20:22
Dernière modification:15 mars 2022 20:22
Afficher les statistiques de telechargements

Éditer le document (administrateurs uniquement)

Creative Commons LicenseSauf indication contraire, les documents archivés dans Constellation sont rendus disponibles selon les termes de la licence Creative Commons "Paternité, pas d'utilisation commerciale, pas de modification" 2.5 Canada.

Bibliothèque Paul-Émile-Boulet, UQAC
555, boulevard de l'Université
Chicoutimi (Québec)  CANADA G7H 2B1
418 545-5011, poste 5630