The occurrence of paragonite in chloritoid schists from Stonehaven, Scotland
نویسنده
چکیده
Paragonite has been found in two chloritoid-chlorite-mica schists from the Dalradian, north of Stonehaven. The principal bulk-chemical constraints on the occurrence of this mineral within the chloritoid zone appear to be the ratios of soda to potash and the A1203 contents of the rock. The composition of paragonite coexisting with muscovite indicates a crystallization temperature of 550 ~ for rocks some way above the chloritoid isograd. Although this result is supported by other mineral equilibria, the muscovite compositions suggest a temperature of 69o ~ which is too high because the mineral assemblage chloritoid-paragonite is unstable above about 6oo ~ By combining data on the breakdown of the chloritoid-paragonite assemblage with a mineral equilibrium for the assemblage garnet-plagioclase-muscovite-biotite, it has been deduced that rocks close to the staurolite isograd crystallized at about 7"5 kb and 6oo ~
منابع مشابه
Distribution of Fe and Mg between garnet and biotite in Scottish Barrovian metamorphic zones
The distribution coefficient KD=(Mg / Fe)garnet/(Mg/Fe)biotite has been calculated for eight garnet-biotite pairs from rocks ranging from the garnet isograd to the staurolite zone along the Stonehaven coast of NE Scotland. This distribution coefficient depends upon metamorphic temperature and is not dependent upon the Mn and Ca content of garnet. Garnet-biotite geothermometer yields temperature...
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