Microstructural analysis of Hole 735B, atlantis bank, Southwest Indian Ridge: Reevaluation of high temperature fabric development

The lower oceanic crust formed at slow-spreading ridges contains abundant (up to ~60%) Fe-Ti oxides, suggesting Fe-Ti oxides are a significant portion of oceanic crust. Dick et al. (2000) have suggested a correlation between Fe-Ti oxide abundance and deformation, with shear zones forming pathways for fractionating melt in oceanic core complexes. Using microstructural analysis on samples from Integrated Oceanic Drilling Program (IODP) Hole 735B Atlantis Bank, Southwest Indian Ridge (SWIR), textures of Fe-Ti oxides were studied to determine the formation, timing, and deformation style of the Fe-Ti oxides, olivine, plagioclase, and pyroxene. The Fe-Ti oxides have different bulk morphology and crystal geometry depending on the abundance of oxides and intensity of deformation. Results suggest that the deformation mechanism of plagioclase (i.e., recrystallization) and pyroxene (i.e., rotation and fracturing) controls the style of Fe-Ti oxide formation. Mineral inclusions in the Fe-Ti oxides suggest forceful intrusion (e.g., diking, brecciation) due to overpressure of a melt zone. Comparison with layered mafic intrusions, for example, textures and correlation with felsic veins, suggests liquid immiscibility plays an important role in the formation of the Fe-Ti oxides.