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Volume 72, Issue 1
Displaying 1-5 of 5 articles from this issue
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AKIRA FUJIYOSHI1977 Volume 72 Issue 1 Pages 1-12
Published: January 05, 1977
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSIn the Donachui River area of the Santa Marta Mountains, Precambrian metamorphic rocks of amphibolite facies and three large Mesozoic masses are exposed. The metamorphism is considered to be associated with a large-scale granitization and probably superimposed on an earlier granulitic facies metamorphism. Many retrogressive minerals are also observed in the metamorphic rocks.
From the obliquities and optics of K-feldspar, the following three events are recognized in the metamorphic process. (1) a hair- or string-perthitic orthoclase (Δ=0, 2VX=59°-65°) was formed during the main phase of metamorphim; (2) this orthoclase was mostly transformed into maximum microcline (Δ=0.84-0.99, 2VX=76°-83°) with grading texture during the cataclastic movement; (3) some orthoclases have been transformed into intermediate microcline (Δ=0.77-0.81, 2VX=68°-72°) and the maximum microcline has been converted into “dirty” microcline (Δ=0.86-0.92, 2VX=76°-85°) showing ambiguous grating texture and containing abundant second generation perthitic albite during the retrogressive metamorphism.
Most K-feldspar in Mesozoic granites is orthoclase.View full abstractDownload PDF (2345K) -
Kin-ichi Sakurai, Michiaki Bunno, Masahiro Aoki, Yasumitsu Suzuki1977 Volume 72 Issue 1 Pages 13-27
Published: January 05, 1977
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSMyokenzan is located in the southern part of the Abukuma metamorphic belt, and consists of dioritic to gabbroic rocks of late Cretaceous intruded in the upper Paleozoic metamorphic members.
The pegmatite body, which is dike or lens in shape, is originated in the gabbroic rock, and is composed of quartz, albite, microcline, muscovite and tourmaline (indigolite). In the central part of the pegmatite body, fine-grained massive lepidolite vein is cutting through, and is associated with elbaite, beryl (Cs-bearing), pollucite, montebrasite and spodumene which is the first discovery in Japan. Spodumene occurs as light grey to grey translucent tabular crystals up to 10cm long and 5mm in thickness, and sometimes forms pseudomorph of hydromuscovite.
Other associated minerals are small amounts of cassiterite (Nb2O5; about 11 wt. %) and mangantantalite.
14 chemical analyses and 16 X-ray powder diffraction data are tabulated.View full abstractDownload PDF (2612K) -
AKIRA ONO1977 Volume 72 Issue 1 Pages 28-29
Published: January 05, 1977
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSChemical composition of Japanese Chichibu geosynclinal sediments have been studied by several investigators (Miyashiro and Haramura, 1962; Banno and Chappell, 1969). The aim of their studies were to determine chemical changes of metamorphic rocks accompanying with regional metamorphism and to find any systematic variations in chemical composition of sediments across the Chichibu geosyncline. Miyashiro and Haramura (1966) showed that pelitic rocks in Hitachi and other regions where volcanic activities were common in Paleozoic geosyncline were poor in K2O and rich in CaO, FeO and MgO compared with the Ryoke metamorphic rocks. They suggested that such a chemical characteristic was a result of mixing of basic volcanic material into pelites.
The present writer determined the concentration of ZrO2 in eleven pelitic rocks and one green stone from the Ryoke and the Sanbagawa metamorphic belts in order to elucidate the relationships between chemical composition of pelites and sedimentary environments.View full abstractDownload PDF (86K) -
TETSUYA SHOJI1977 Volume 72 Issue 1 Pages 30-41
Published: January 05, 1977
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe stability field of grossular in H2O-CO2 mxitures has been calculated on the basis of previous work in the system CaO-A12O3-SiO2-H2O-CO2. The following reactions restricting the grossular field are, from high to low temperatures:
(1) grossular+CO2=calcite+anorthite+wollastonite
(2) grossular+CO2=calcite+anorthite+quartz
(3) grossular+CO2+H2O=calcite+zoisite+quartz
(4) grossular+CO2+H2O=calcite+prehnite.
These reactions give three isobaric invariant points, that is, point A (calcite-wollastonite-grossular-anorthite-quartz): T=564°C and XCO2=18.8 mole % at 1000 bars, and T=575°C and XCO2 =13.9 mole % at 2000 bars; point B (calcite-grossular-zoisite-anorthite-quartz): T=461°C and XCO°C=5.18 mole % at 1000 bars, and T=503°C and XCO2=6.30 mole % at 2000 bars; and point C (calcite-grossular-zoisite-prehnite-quartz): T=406°C and XCO2=1.60 mole % at 1000 bars, and T=405°C and XCO2=0.919 mole % at 2000 bars.
In the system containing iron, at the temperatures where the assemblage prehniteiron oxide is not stable, the reaction.
(3') grandite+CO2+H2O=calcite+epidote+quartz+hematite (or magnetite), places the strict limit on the condition of formation of grandite garnet growing in equilibrium with a H2O-CO2 fluid. The upper and lower limits on the carbon dioxide conditions of formation of ore-bearing skarn consisting of calcite, grandite and quartz are approximately placed by Reaction (3') and the reaction,
calcite+quartz=wollastonite+CO2
respectively.View full abstractDownload PDF (499K) -
Ichiro SUNAGAWA1977 Volume 72 Issue 1 Pages 42-43
Published: January 05, 1977
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSDownload PDF (78K)
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