Metamorphic history of garnet glaucophane schists, sodic pyroxene-bearing quartz schists and pelitic schists from the Bizan area, eastern Shikoku is discussed. The phengites separated from the garnet glaucophane schists and host pelitic schists yielded K-Ar ages of 109 ± 3 Ma and 68 ± 1.7 Ma, respectively. The geologic significance of the ages are also discussed.
The Seba area in the central part of the Besshi district is composed of the Sebadani metagabbro mass and surrounding Seba basic schists. Eclogitic assemblages are sporadically preserved in both the Sebadani metagabbro and the Seba basic schists. The eclogites exposed in the northeastern part of the Seba basic schists consist mainly of garnet, epidote, amphibole, omphacite, phengite. Minor amounts of albite, carbonates, rutile, titanite, biotite, chlorite and quartz. P-T pseudosection in the MnNCKFMASCHO model system using the fractionated bulk composition suggests the conditions of 650-670 °C and 21-22 kbar in the eclogite facies.
This study present a new discovery of the common occurrence of lawsonite-bearing veins from the prehnite-stable unit of the Northern Chichibu belt in central Shikoku. Textural relations show that lawsonite-bearing veins were formed during prograde stages via the reaction laumontite = lawsonite + 2quartz + 2H2O, whereas prehnite-bearing veins were formed during peak-pressure and subsequent decompression stages.
Study area is located in the Neldy Formation, Makbal Complex, Kyrgyz Northern Tien-Shan. White mica in garnet and chloritoid-bearing pelitic schists shows zoning, phengite core and muscovite rim and white mica in pelitic schist shows core and rim is phengite. Obtained white mica K-Ar age of 474±12 Ma for garnet and chloritoid-bearing pelitic schists and age of 524±13 Ma pelitic schists. The age 524 represent high P/T metamorphism as first high-pressure metamorphism in the garnet and chloritoid-bearing pelitic schists. The age of 474 Ma is a mixed age corresponds as high pressure metamorphism and amphibolite facies metamorphism.
An eclogite collected from the Bohemian Massif contains leucocratic veins that mainly consist of plagioclase. Melanocratic part of the eclogite mainly comprises of garnet, clinopyroxene and rutile. The leucocratic veins also contain garnet and clinopyroxene. Garnet and clinopyroxene in the leucocratic veins display faceted shapes while those in the melanocratic part show irregular shapes. This probably suggests that the leucocratic veins were originally melt. Clinopyroxene shows approximately the same major- and trace-elements composition between grains in the melanocratic part and faceted shape grains in the leucocratic veins. These suggest that the melt was formed by partial melting of this eclogite.
Some garnet peridotites collected from the Bohemian Massif have shown pressures more than 4GPa. In this study, we newly found phlogopite-bearing peridotite. Large garnets with phlogopite inclusions yielded P-T conditions of 1200-1300oC, 5.5GPa, whereas small garnets yielded P-T conditions less than 1000oC, 4GPa. Existence of spinel inclusions in garnet suggests that the peridotites were under low-P conditions and then experienced increase of pressure prior to the above maximum P-T stage. K in the phlogopite inclusions was possibly supplied from the surrounding gneiss. The peridotite and gneiss may have experienced the same peak P-T conditions.
We studied amphiboles in some eclogites from the Su-Lu region and classified them into three types ; Amp I inclusions in Grt., Amp II(Na-Ca Amp): large grains in matrix.,Amp III: small grains developed along grain boundaries. Amp II is higher in NaB than Amp III and Amp I. NaB of Amp I continuously varies to that of Amp II. Thus Amp I formed during compression, and Amp II was stable at the peak P-T stage. P-T conditions were estimated as 500–700oC, 2.0–3.5 GPa. Therefore, we conclude that Na-Ca Amp was stable under UHP-HP conditions.
Major components and salinity of fluid inclusions in jadeitites were examined. The fluid inclusions consist of H2O ± CH4. The salinity is 7-8 wt% NaCl equivalent in the quartz-free jadeitites and is typically about 5 wt% NaCl equivalant in the quartz-bearing jadeitites. This result suggests that salinity of fluid decreases with depth in subduction zones.