Orthopyroxene-bearing basic metamorphic rock occurs as a block enclosed within pelitic-psammitic metamorphic rock in the Ina district of the Ryoke belt. The orthopyroxene is irregular in shape and includes many rounded crystals of calcic amphibole and plagioclase. Orthopyroxene is a representative metamorphic mineral of the granulite facies for rocks of basic composition and a number of metamorphic reactions to produce orthopyroxene have been proposed. However, none of the metamorphic reactions is consistent with the observed textural relationships and the mineral paragenesis of the rock. The author, therefore, suggests that the orthopyroxene was formed by a distinct process. A simple hypothesis to account for the occurrence of the orthopyroxene is that the orthopyroxene was crystallized after a process of partial melting, i.e., melt produced by partial melting was distributed along grain boundaries of calcic amphibole and plagioclase, and this melt precipitated the orthopyroxene. This hypothesis is supported by the following facts: 1) The texture of the orthopyroxene is unusual for a metamorphic mineral. 2) No simple process other than the crystallization from a partial melt fraction can consistently account for the mode of occurrence of orthopyroxene. 3) Recent experimental results suggest that partial melting of basic rock can take place at the temperatures in the high-grade parts of the Ryoke belt, and furthermore that orthopyroxene is a likely product of such partial melting.

View full abstract

The REE distribution in ferromanganese oxide ores from Iron Ore Group, Western Koira valley India, are studied. Mn-ores in the region generally occur as stratabound and lateritoid: bodies, showing remarkable similarity in their mineral assemblages and having contrasting REE signature. The stratabound ores show higher concentration of both LREE (208 to 640 ppm) and HREE (121 to 285 ppm) as compared to that of the lateritoid types. Similar Chondrite and Shale normalized REE profiles in different deposits suggest a common mode of Mn-mineralization in the area. However variable La/Lu, La/Yb and Nd/Sm ratios attest to significant LREE fractionation in lateritoid deposits. Intense lateritization resulting in oxidation and weathering, mobilization and fractionation, has caused two distinct REE domains in the Koira valley region, India.

View full abstract

The Rb-Sr chronology of three granitic bodies (Inutagiri, Otagiri and Nakatagiri) which comprise the Otagiri granites has been examined. Whole-rock, biotite and a felsic fraction separated from one sample from each granitic body gave Rb-Sr isochron ages of 52.2±0.5 Ma (Inutagiri), 54.7±0.1 Ma (Otagiri) and 54.6±0.4 Ma (Nakatagiri). Muscovite separated from the Inutagiri sample did not plot on the whole-rock and mineral isochron, but gave a Rb-Sr whole-rock and muscovite isochron age of 67.5±0.02 Ma. However, muscovite separated from the Nakatagiri sample plotted on the whole-rock and mineral isochron. The cooling process of these granitic bodies was evaluated using these ages and previously published Rb-Sr whole-rock isochron determinations. The Inutagiri granitic body cooled at about 19°C/Ma from the time of emplacement to about 310°C. The Otagiri and Nakatagiri granitic bodies were kept at high temperature. The Otagiri granitic body cooled in a similar fashion to the Inutagiri granitic body after 70 Ma. The cooling of these bodies was caused by finish of igneous activity and uplifting of the metamorphic belt. Considering the difference between the whole-rock and mineral isochron ages of the Otagiri granites and those of the Katsuma quartz diorite, the southeast side of the Ryoke belt in the Ina district might uplift and cool down earlier than other area.

View full abstract

The St. Xavier Chapel built in 1890, Kyoto, Japan, was moved to the Museum Meiji-Mura in 1965. In the Chapel, there are fourteen oil paintings called “Via Crucis” painted on metal plate. Among them, ten works have been restored since 1989. During restoration, paint fragments were sampled and researched by mineralogical methods: observation of cross-sections by an optical microscope, and identification of pigments by EPMA. Main materials of the white ground layer are barite (Ba_0.96Sr_0.04) SO₄ and hyrdocerrusite. In the painting layer, hydrocerrucite was also used as a white pigment. For the other colors, hematite, goethite, illite, ultramarine blue (lazurite), vermillion (cinnabar) and carbon and ivory black were found. The hydrocerrusite, ultramarine, vermillion and carbon and ivory black are considered as synthetic pigments. Between the white ground layer and the metal plate, a green transparent oil layer containing copper and zinc was observed. This layer may be formed as a result of a chemical reaction between the oil and the metal plate. Based on the ratio of copper and zinc, the metal plate is considered as of a brass. Before the restoration, the surface of the works appeared pale green to the naked eye. There are two possibilities for the reason: one is the migration of green oil to the surface and the other is the glazing effect of the yellowing varnish and the black pigments having alittle blue color.

View full abstract