日高変成帯, 静内川地域に産する十字石 Staurolite occurrences in the Shizunai river area in the Hidaka metamorphic belt, Hokkaido, Japan
A new staurolite locality in the Hidaka metamorphic belt (HMB) is reported. Staurolite occurs as inclusions in garnet and plagioclase in alternating garnet-cordierite and garnet-cordierite-gedrite gneisses in the Shizunai river area, central part of the belt.<br> Two types of staurolite-breakdown reactions, Staurolite+Chlorite+Quartz=Garnet+H<sub>2</sub>O and Staurolite+Gedrite (Na-, Al-poor)+Plagioclase (Ca-poor)=Gedrite (Na-, Al-rich)+Plagioclase (Ca-rich)+Quartz+H<sub>2</sub>O, are recognized. Subsequently, Gedrite (Na-rich)+Plagioclase (Ca-rich)+Quartz=Gedrite (Na-poor)+Plagioclase (Ca-poor) occurred.<br> Estimated H content of the staurolite is low (2.2-3.2), suggesting low pressure type. Those from the both Menashunbetsu river and Hidakahorobetsu river areas, locating in the south of the Shizunai river area, show similar values.<br> Fe-Mg partitioning coefficients between included staurolite and host garnet are plotted on and around the line of K<sub>D</sub> =1. Despite of large uncertainty (±60-70°C) of the Koch-Müller (1997)'s staurolite-garnet geothermometry, the application to the pair from the Shizunai river area shows a consistent result with other methods. The minimum temperature estimate for staurolite-garnet pairs is almost constant through the whole HMB. The closure temperature of the Fe-Mg exchange reaction between staurolite and garnet in the HMB is ca. 700°C.<br> The similarities of H contents of staurolite and Fe/Mg distribution and re-equilibration processes of staurolite-garnet pairs may indicate that at least high-grade part of the central area of HMB has been suffered similar thermal histories at similar depths.
- 岩鉱 : 岩石鉱物鉱床学会誌 : journal of mineralogy, petrology and economic geology
岩鉱 : 岩石鉱物鉱床学会誌 : journal of mineralogy, petrology and economic geology 94(8), 267-278, 1999-08
Japan Association of Mineralogical Sciences