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TitreZircon textures and composition: refractory recorders of magmatic volatile exsolution?
AuteurErdmann, S; Wodicka, N; Jackson, S E; Corrigan, D
SourceContributions To Mineralogy and Petrology 2012., https://doi.org/10.1007/s00410-012-0791-z
Année2012
Séries alt.Secteur des sciences de la Terre, Contribution externe 20110040
Documentpublication en série
Lang.anglais
DOIhttps://doi.org/10.1007/s00410-012-0791-z
Mediaen ligne; numérique
Formatspdf
ProvinceNunavut
SNRC46N/01; 46N/02; 46N/03; 46N/06; 46N/07; 46N/08; 46N/09; 46N/10; 46N/11; 46O/04; 46O/05; 46O/12
Lat/Long OENS-85.5000 -83.5000 67.7500 67.0000
Sujetsaltération; produits d'altération; roches ignées; roches plutoniques; granites; magmas; dynamique des fluides; fluage; mécanique des fluides; migration des fluides; zircon; datations au zircon; analyses de textures; analyses géochimiques; pétrologie ignée et métamorphique; géochimie
Illustrationslocation maps; tables; photomicrographs; plots
ProgrammeGisements polymétalliques - Presqu'île Melville (Nunavut), GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Zircon textures and composition have been used to infer magmatic processes including closed-system fractional crystallization, magma mixing or replenishment, and country-rock assimilation. Here, we propose that zircon textures and composition may also be refractory recorders of magmatic volatile evolution. We present field, whole-rock chemical, textural, mineral chemical, and U - Pb age data from evolved, fine-to-coarse-grained granite intrusions on Melville Peninsula, Nunavut, Canada. Zircon forms two main populations in these granites, Type-1 and Type-2 zircon. Type-1 zircon is present in all samples, but predominant in fine-grained granite. Crystals are euhedral and inclusion-rich and show periodic, fine-scale oscillatory zoning, comparatively low concentrations of U (<2,200 ppm) and Hf (<1.6 wt%), high Zr/Hf (~40 - 62), and pervasive alteration. Type-2 zircon is predominant in coarse-grained granite. Crystals form overgrowths on Type-1 zircon and individual crystals. They are subhedral and inclusion-poor and show weak, irregular, large-scale oscillatory zoning, high U (up to ~7,250 ppm) and Hf (1.5 - 2.0 wt%), low Zr/Hf (~37 - 44), and only local alteration. Compatible trace-element concentrations and Zr/Hf change sharply across the boundary of Type-1 to Type-2 zircon; 207Pb/206Pb ages preclude a significant hiatus between crystallization of the two types. We argue against magmatic versus hydrothermal crystallization, country-rock assimilation, or magma mixing as causes for the crystallization of Type-1 and Type-2 zircon. We propose instead that Type-1 zircon formed from volatile-undersaturated magmas and that Type-2 zircon formed from volatile-saturated magmas. Magmas fractionated by volatile-driven filter pressing into crystal-rich mush and crystal-poor magma. Crystal-rich mush with abundant Type-1 zircon crystallized to fine-grained granite. Volatile-rich magma crystallized to Type-2 zircon and coarse-grained granite. While Type-1 zircon was pervasively altered by exsolving magmatic volatiles, Type-2 zircon was only locally affected by subsolidus hydrothermal alteration.
GEOSCAN ID288653