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| Titel |
Magma chamber processes inferred from plagioclase composition: The Sept Iles layered intrusion, Canada |
| VerfasserIn |
Olivier Namur |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250075584
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| Zusammenfassung |
| The Sept Iles intrusion (Quebec, Canada) is dominated by a basal Layered Series made up of troctolites and gabbros, and by anorthosite occurring at the roof of the magma chamber (100–500 m-thick) and forming the Upper Border Series. Plagioclase composition and plagioclase compositional profiles from the Layered Series and the Upper Border Series will be used to (1) investigate the origin of anorthosite in Sept Iles and (2) evaluate the mechanism of intercumulus liquid mobility in the Layered Series.
Anorthosite rocks are made up of plagioclase, with minor clinopyroxene, olivine and Fe–Ti oxide minerals. Plagioclase displays a very restricted range of compositions for major elements, trace elements and Sr isotopic ratios. This compositional range is identical to that observed in troctolites, the most primitive cumulates of the Layered Series, whereas plagioclase in layered gabbros is more evolved. The origin of Sept Iles anorthosites is investigated by calculating the density of plagioclase and that of the evolving melts. The density of the FeO-rich tholeiitic basalt parent magma first increased from 2.70 to 2.75 g/cm3 during early fractionation of troctolites and then decreased continuously to 2.16 g/cm3 with fractionation of Fe–Ti oxide-bearing gabbros. Plagioclase (An69–An60) was initially positively buoyant and partly accumulated at the top of the magma chamber to form the roof anorthosite. With further differentiation, plagioclase (
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