DISTRIBUTION OF Ca IN ZONED GARNET OF LOW-GRADE PELITIC SCHISTS

Stability and paragenesis of Fe-Ti oxide minerals and sphene in the basic schists of the Sanbagawa metamorphic belt in central Shikoku, Japan.

“…Although the majority of mineralogy of the Sanbagawa schists is attributable to a single event of progressive metamorphism, disequilibrium parageneses occur not uncom monly in small domains in thin section (Kurata, 1972;Higashino, 1975;Itaya and Banno, in prep;Otsuki and Banno, in prep.). Therefore, as proposed by Itaya Modes of the minerals were measured by the method by Itaya and Banno (in prep.…”

Notes on petrography and rock-forming mineralogy. 5. Reverse-zoned garnet in Sanbagawa pelitic schists in central Shikoku, Japan.

“…Thus, no probable mechanism of the forma tion of reverse-zoned garnets described here can be proposed, but it still is important to recognize that not all of the garnets in the Sanbagawa pelitic schists is simply normally zoned as hitherto considered (of. Banno and Kurata, 1972;Higashino, 1975).…”

Chemical zoning of pegmatite garnets from the Ishikawa and Yamanoo areas, northeastern Japan.

“…The most characteristic feature of the chemical zoning in garnet is the compositional pattern of Ca: the Ca content of garnet I-a increases from the core toward the margin and then decreases again at the rim. Such a compositional pattern of Ca has also been noted for some metamorphic garnets (Banno and Kurata, 1972) and pegmatite garnets (Leake, 1967), which indicates that the pattern is not uncommon. Y contents were determined only for garnets in the Ishikawa rare-element pegmatites (Fig.…”

“…There are a number of studies done on the compositional growth zoning of metamorphic garnets (e.g., Hollister, 1966;Banno and Kurata, 1972;Tracy et al, 1976;Dempster, 1985) since such zoning provides key constraints on the metamorphic processes. Likewise, the chemical zoning of garnet in granitic pegmatite may offer a great deal of information on the genesis of peg matite and the evolution of granitic magma.…”