Heterogeneous distribution of Fe in olivine grains generated by serpentinization
Abstract
We investigated Fe-rich stripes developed within olivine crystals composed of serpentinized peridotites which were obtained at Conical seamount in the Mariana forearc. Modal analyses of primary minerals and their serpentinized pseudomorphs indicate that the protoliths of the peridotites are harzburgite and dunite. They are composed of serpentine minerals, acicular diopside, olivine, magnetite, and rare brucite as metamorphic minerals, and olivine, diopside, and chromian spinel as primary minerals. Chrysotile and/or lizardite are main serpentine minerals, but antigorite is widely distributed in the samples. Forsterite composition of the olivine is Fo90-92. Fe-rich stripes with ca. 5 um width are well developed within the olivine crystals. The distribution of the Fe-rich stripes is restricted only at the area contacted with antigorite. TEM samples made using the Focused Ion Beam system indicate clearly that the Fe-rich stripes are created on the dislocation arrays making (100) sub-grain boundaries. Forsterite composition on the dislocation arrays measured by ATEM and EPMA is ca. 88 mol%. These facts can be explained by interdiffusion between Mg and Fe along the dislocation core during serpentinization after ceasing plastic deformation of olivines. The origin of high Fe composition is probably olivine itself, because the antigorite formation causes an extra Fe. This phenomenon is much important to understand the behavior of fluid and composition during serpentinization.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMMR33A1662A
- Keywords:
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- 3620 MINERALOGY AND PETROLOGY / Mineral and crystal chemistry;
- 3621 MINERALOGY AND PETROLOGY / Mantle processes;
- 3625 MINERALOGY AND PETROLOGY / Petrography;
- microstructures;
- and textures;
- 8030 STRUCTURAL GEOLOGY / Microstructures