A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)

Détails

ID Serval
serval:BIB_F8E029D98F94
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Titre
A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)
Périodique
Contributions to Mineralogy and Petrology
Auteur(s)
Dessimoz M., Muntener O., Ulmer P.
ISSN-L
0010-7999
Statut éditorial
Publié
Date de publication
2012
Peer-reviewed
Oui
Volume
163
Pages
567-576
Langue
anglais
Résumé
Amphibole fractionation in the deep roots of subduction-related magmatic arcs is a fundamental process for the generation of the continental crust. Field relations and geochemical data of exposed lower crustal igneous rocks can be used to better constrain these processes. The Chelan Complex in the western U. S. forms the lowest level of a 40-km thick exposed crustal section of the North Cascades and is composed of olivine websterite, pyroxenite, hornblendite, and dominantly by hornblende gabbro and tonalite. Magmatic breccias, comb layers and intrusive contacts suggest that the Chelan Complex was build by igneous processes. Phase equilibria, textural observations and mineral chemistry yield emplacement pressures of similar to 1.0 GPa followed by isobaric cooling to 700 degrees C. The widespread occurrence of idiomorphic hornblende and interstitial plagioclase together with the lack of Eu anomalies in bulk rock compositions indicate that the differentiation is largely dominated by amphibole. Major and trace element modeling constrained by field observations and bulk chemistry demonstrate that peraluminous tonalite could be derived by removing successively 3% of olivine websterite, 12% of pyroxene hornblendite, 33% of pyroxene hornblendite, 19% of gabbros, 15% of diorite and 2% tonalite. Peraluminous tonalite with high Sr/Y that are worldwide associated with active margin settings can be derived from a parental basaltic melt by crystal fractionation at high pressure provided that amphibole dominates the fractionation process. Crustal assimilation during fractionation is thus not required to generate peraluminous tonalite.
Création de la notice
28/09/2012 22:41
Dernière modification de la notice
03/03/2018 22:53
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