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＜departmental bulletin paper＞
Omphacite-bearing reaction zone in the Nagasaki metamorphic rocks, the Nomo peninsular
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| Abstract | This paper describes an omphacite-bearing reaction zone developing between serpentinite and taramite-rich metabasite from Nomo, Nagasaki Prefecture. The reaction zone consists of four subzones: tremol...ite-serpentine zone, tremolite-chlorite zone, chlorite zone, and omphacite zone from serpentinite towards metabasite. The metabasite is composed of magnesio-taramite, albite, epidote, and minor omphacite. Quartz does not occur both in the metabasite and in the omphacite zone. Clinopyroxene in serpentinite is completely replaced by tremolite around the reaction zone. Modal analysis and textural evidence of the rocks from subzones suggest the reaction 2 Taramite+ 2 Albite+ 2 Epidote= 12Omphacite+ 5 Al_2O_3 +3H_2O which is coupled with the reaction: 11 Serpentine+2Diopside+6A l_2O_3H_2O=6Chlorite+Tremolit through diffusion of Al_2O_3. Thus, the driving force for the omphacite-formation is the difference of chemical potential of Al_2O_3 (not SiO_2) between serpentinite and the metabasite. This idea is supported by the analysis of chemical potential gradient indicating no difference of SiO_2-potential between the omphacite zone and the metabasiteshow more |
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| Created Date | 2021.10.25 |
| Modified Date | 2022.06.20 |