Major and trace element chemistry of the garnets within the Sambagawa pelitic schists in the Asemigawa area, central Shikoku, Japan

その他

Garnets within the Sambagawa pelitic schists show distinct major and trace element zoning．The chemical compositions of the major（Mn，Fe，Mg and Ca）and trace（Na，Ti，Cr，V，Sc，Y，Er and Yb）elements in the garnets were determined using an electron probe microanalyzer（EPMA）．
The pelitic schists analyzed were collected from the garnet zone，through the albite-biotite zone，up to the oligoclase-biotite zone．The cores of garnets in the garnet zone are higher in Mn/（Mn＋Fe＋Mg）that in the albite- and oligoclase-biotite zones．In the albite- and oligoclase-biotite zones，the maximum Mn/（Mn＋Fe＋Mg）at the cores of the garnets are almost the same．Mg/（Mn＋Fe＋Mg）at the outermost rims of the garnets increases with increasing metamorphic grade．The maximum Mg/（Mn＋Fe＋Mg）value is 0.07 for the garnet zone，0.08 for the albite-biotite zone（lower），0.11 for the albite-biotite zone（upper），and 0.16 for the oligoclase-biotite zone．
In the garnets within the pelitic schists in the Asemigawa area，the maximum abundances of Na，Y，Er and Yb contents generally occur in the core，and their contents decrease towards the rim．There are，however，extremely high-trace element
（Na，Y，Er and Yb）zones in the mantle of the garnets．In some garnets，the trace element contents in these zones are more than ten times higher than that of the surrounding mantle．