Dizhi lixue xuebao (Oct 2021)
Anatexis and enrichment mechanism of the Fe-Ti oxide minerals in the quartzofeldspathic gneisses from the Larsemann Hills, East Antarctica
Abstract
Fe-Ti oxide minerals can be locally aggregated or enriched in the quartzofeldspathic gneisses from the Larsemann Hills, East Antarctica. The enrichment is related to anatexis and subsequent high-grade metamorphism, not inherited from the protolith. The partial melting process was responsible for the residues or local enrichment of the inert Fe-Ti-Al elements and the migration of mobile components, and the volatiles were preferentially incorporated in the melt. In the water-deficient system, the local "melt" in anatexis crystallized to form the leucosomes without melt texture or minimum eutectic composition, suggesting the meta-melt feature, not real melt. The coarse leucosome or pegmatite occurred in anataxis as pre-granitic vein or body and had nothing to do with the late stage differentiation of the granitic magma. Together with the presence of the meta-melt, the substantial differentiation of the components resulted in solid residues and corresponding meta-melt phases, with the former enriched in Al, Fe elements and sillimanite, Fe-Ti oxide minerals occurred. On the contrary, the leucosomes with possible short distance migration of components were poor in Fe, Ti compositions, and seldom formed garnet and Fe-Ti oxides. The volatile-unsaturated anatexis was an essentially closed system and the total dehydration effect was not obvious. The presence of some typical minerals in high-grade metamorphism of the quartzofeldspathic gneisses, such as sillimanite, garnet, cordierite and spinel, was derived from component differentiation in partial melting of the rocks. However, the components migration was limited, and the evolving stages of metamorphism and differentiation could be preserved. Voluminous Fe-Ti oxides and sillimanite in the quartzofeldspathic gneisses suggest the possible local or differential uplifting of the area, the heterogeneity of deformation and accompanying components differentiation, corresponding to the reactivation of the earlier structures in the Pan-African event.
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