16:30 〜 16:45
[SMP24-11] Metasomatic Corundum-Sapphirine-Spinel-Clinozoisite assemblage Indications for Ca-Al rich fluid
キーワード：Metasomatism, Sapphirine, Al-Ca fluid
Sapphirine-spinel assemblage is typical in Mg-Al rich silica undersaturated ultrahigh temperature granulites. However, clinozoisite is an epidote series mineral with low to medium grade regional metamorphic or in contact metamorphic region. Corundum is usually present in silica undersaturated highly aluminous rocks. Hence it is difficult to form these minerals together unless in typical conditions or settings.
Here we report a Corundum-Sapphirine-Spinel-Clinozoisite vein with or without Ti-free högbomite from Manavadi near the Palghat-Cauvery-Shear zone in southern India. Sapphirine is identified as inclusions only within the spinel. Spinel grains are porphyroblasic and associated with clinozoisite-plagioclase assemblage along the fracture boundary associated with the host amphibolite. Högbomite is present as a later phase associated with spinel grain boundary. Spinel and clinozoisite form a partial rim around the corundum. In few other domains of the same rock consist of spinel corona over corundum and spinel growth along the amphibole grain boundaries associated with a calcite vein.
The spinel is Fe-Mg rich with slightly rich in Mg (XMg = 0.67) composition. Sapphirine is peraluminous with a composition near to 7:9:3 or even more aluminous. Sapphirine present in garnet-orthopyroxene or quartz-bearing Mg-Al rich granulite is more silica-rich. The host amphibolite is a calcium-rich sample with only clino-amphibole and plagioclase as mineral assemblage.
Based on the textural association, P-T estimates, and fluid composition, we demonstrate that sapphirine bearing assemblage formed through metasomatic reactions between a Ca-Al rich fluid and the host amphibolite. The corollary of our observation also indicates the immobile elements like aluminum can dissolve as salt in aqueous fluids and become mobile to form unique mineral assemblages. The present study also caution that many of the UHT assemblages may be resulted from metasomatic reactions that lead to misinterpretation.
Here we report a Corundum-Sapphirine-Spinel-Clinozoisite vein with or without Ti-free högbomite from Manavadi near the Palghat-Cauvery-Shear zone in southern India. Sapphirine is identified as inclusions only within the spinel. Spinel grains are porphyroblasic and associated with clinozoisite-plagioclase assemblage along the fracture boundary associated with the host amphibolite. Högbomite is present as a later phase associated with spinel grain boundary. Spinel and clinozoisite form a partial rim around the corundum. In few other domains of the same rock consist of spinel corona over corundum and spinel growth along the amphibole grain boundaries associated with a calcite vein.
The spinel is Fe-Mg rich with slightly rich in Mg (XMg = 0.67) composition. Sapphirine is peraluminous with a composition near to 7:9:3 or even more aluminous. Sapphirine present in garnet-orthopyroxene or quartz-bearing Mg-Al rich granulite is more silica-rich. The host amphibolite is a calcium-rich sample with only clino-amphibole and plagioclase as mineral assemblage.
Based on the textural association, P-T estimates, and fluid composition, we demonstrate that sapphirine bearing assemblage formed through metasomatic reactions between a Ca-Al rich fluid and the host amphibolite. The corollary of our observation also indicates the immobile elements like aluminum can dissolve as salt in aqueous fluids and become mobile to form unique mineral assemblages. The present study also caution that many of the UHT assemblages may be resulted from metasomatic reactions that lead to misinterpretation.