Iron-titanium oxide minerals in the Upper Layered
SUMMARY. Electron-probe data are presented for coexisting magnetite and ilmenite from seven gabbro cumulates and a gabbro pegmatite, and bulk FeO-F%O3-TiO2 analyses for ten magnetite-ilmenite assemblages. The oxides equilibrated at 58o o 72o ~ and oxygen fugacities of IO-1~'0 to to-20.5 bar. La...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.629.4132 http://www.minersoc.org/pages/Archive-MM/Volume_38/38-300-946.pdf |
| Summary: | SUMMARY. Electron-probe data are presented for coexisting magnetite and ilmenite from seven gabbro cumulates and a gabbro pegmatite, and bulk FeO-F%O3-TiO2 analyses for ten magnetite-ilmenite assemblages. The oxides equilibrated at 58o o 72o ~ and oxygen fugacities of IO-1~'0 to to-20.5 bar. Late-stage alteration, associated with growth of hydrot ermal silicates, resulted in the breakdown of ilmenite to rutile and the dissolution f magnetite. Higher levels in the intrusion equilibrated at lower temperatures than deeper levels. All features described are consistent with the retention of the initial water content of the magma within the walls of the intrusion. THE Upper Layered Series of the Kap Edvard Holm complex consists of plagioclase-augite-magnetite and plagioclase-augite-olivine-magnetite orthocumulates. The presence, throughout the exposed succession, of cumulus magnetite indicates a high Fe3+: Fe 2+ ratio in the crystallizing magma and this is considered to be the result of a high water content. Other features associated with the high water content are, firstly, the ubiquitous occurrence of pargasitic amphibole as a primary crystallizing phase; secondly, exten-sive hydrothermal teration of the primary minerals over a wide range of temperature |
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