Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro
- Author(s)
- Ge Bian, Olga Ageeva, Aleksander Rečnik, Gerlinde Habler, Rainer Abart
- Abstract
Plagioclase hosted needle- and lath-shaped magnetite micro-inclusions from oceanic gabbro dredged at the mid-Atlantic ridge at 13° 01–02′ N, 44° 52′ W were investigated to constrain their formation pathway. Their genesis is discussed in the light of petrography, mineral chemistry, and new data from transmission electron microscopy (TEM). The magnetite micro-inclusions show systematic crystallographic and shape orientation relationships with the plagioclase host. Direct TEM observation and selected area electron diffraction (SAED) confirm that the systematic orientation relations are due to the alignment of important oxygen layers between the magnetite micro-inclusions and the plagioclase host, a hypothesis made earlier based on electron backscatter diffraction data. Precipitation from Fe-bearing plagioclase, which became supersaturated with respect to magnetite due to interaction with a reducing fluid, is inferred to be the most likely formation pathway. This process probably occurred without the supply of Fe from an external source but required the out-diffusion of oxygen from the plagioclase to facilitate partial reduction of the ferric iron originally contained in the plagioclase. The magnetite micro-inclusions contain oriented lamellae of ilmenite, the abundance, shape and size of which indicate high-temperature exsolution from Ti-rich magnetite constraining the precipitation of the magnetite micro-inclusions to temperatures in excess of~600 °C. This is above the Curie temperature of magnetite, and the magnetic signature of the magnetite-bearing plagioclase grains must, therefore, be considered as the thermoremanent magnetization.
- Organisation(s)
- Department of Lithospheric Research
- External organisation(s)
- Jožef Stefan Institute (IJS)
- Journal
- Contributions to Mineralogy and Petrology
- Volume
- 176
- No. of pages
- 21
- ISSN
- 0010-7999
- DOI
- https://doi.org/10.1007/s00410-021-01864-8
- Publication date
- 12-2021
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105115 Magnetics, 105113 Crystallography, 105120 Petrology
- Keywords
- ASJC Scopus subject areas
- Geochemistry and Petrology, Geophysics
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/99137f78-c3ca-4de5-9ae0-63e7591faa95