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Volume 76, Issue 2
Displaying 1-4 of 4 articles from this issue
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PART II: HUDROTHERMAL EVENTS AND GENESIS OF IGNEOUS ALBITETAKASHI AGATA1981 Volume 76 Issue 2 Pages 35-48
Published: February 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe Main Appinitic Sequence is a suite of hornblende-rich gabbroic and dioritic rocks, late differentiates of the õura Igneous Complex. Hydrothermal minerals including hornblende, epidote, biotite, plagioclase, and quartz are spread out in the Main Appinitic Sequence, and they form such mineral assemblages as hornblende-rich, epidote-rich, and biotite-rich. An appreciable amount of copper sulfide concentration occurs in a biotite-rich altered area. Fluid inclusions in the quartz crystals from the mineralized area show fairly high homogenization temperatures, suggesting that the mineralization and alteration were caused essentially by fluid which escaped from the magma forming the Main Appinitic Sequence. The variation of hydrothermal assemblages may be the result of fractional separation of fluid: the earlier separated fluid brings about the hornblende-rich and epidoterich assemblages in the earlier formed appinitic rocks, and the biotite-rich assemblage and copper sulfide concentration in leuco albite tonalite are formed by the fluid escaping from the later differentiated magma.
The albite with the igneous textures from the Main Appinitic Sequence is sometimes replaced by the hydrothermal calcic plagioclase and presumably is an original product crystallized from the magma. The generation of albite may be accounted for by the large amount of hornblende concurrently crystallizing from the magma: in view of incongruent melting of hornblende, hornblende in liquid comes out at the expense of anorthite, clinopyroxene, and orthopyroxene components in the final stage of crystallization of clinopyroxene and brings down the activity of anorthite in liquid.View full abstractDownload PDF (1091K) -
HIROMITSU TANIGUCHI1981 Volume 76 Issue 2 Pages 49-57
Published: February 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe glass transformation temperature (Tg) of rhyolitic rock melt was considerably influenced by the content of water in the melt. Tg determined by means of the differential thermal analysis-thermogravimetric analysis under various experimental conditions ranged from 490° to 760°, and decreased linearly with increasing water content in the melt at Tg. The experimental equation for the relation was Tg=778-223WH2O. The decrease of Tg with the increase of water may be explained by a decrease of the degree of polymerization of silicate anions in the rock melt as was analogized from the case of organic polymer solution.
In the experiments under the same conditions (sample grain size, heating rate), a strong correlation was observed between Tg and water released between Tg and 950°C. On the other hand, it was difficult to find a certain relationship between Tg and water released at above 950°C. These results can be explained in terms of the difference of the force constant of OH bonding of water. The water which had a smaller force constant dissociated from the melt structure at lower temperature, moved freely among the melt structure and destroyed Si-O-Si bonds by the collision with the bonds. Thus the water had a direct effect upon Tg.View full abstractDownload PDF (607K) -
HARUO OHASHI, TAKETOSHI FUJITA, TOSHIKAZU OSAWA1981 Volume 76 Issue 2 Pages 58-60
Published: February 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe crystal structure of Co3Al2Si3O12 granet grown by the hydrothermal method has been refined by the least squares method using 635 reflections measured on an automatic single crystal diffractometer. The unweighted R factors is 0.037 for 469 unrejected reflections, of which 259 are non-equivalent. The cell dimensions are: a0=11.455 Å, and V=1503.07Å3; space group Ia3d. The Si-O distance is 1.627(2)Å.
Comparison of a new crystal structure refinement for Co3A12Si3O12 garnet with published refinements for some alumino silicate garnets indicates that the Si-O bond lengths correlate with electronegativity of non-tetrahedral cations as two separate trends. One is pyropegrossular series and the other is Co3Al2Si3O12 garnet-almandine-spessartine series. In the former their dodecahedral sites are mainly occupied by M2+cations which have empty 3d orbitals, whereas in the latter the dodecahedral sites are mainly or partially occupied by M2+ cations which have no empty 3d orbitals.View full abstractDownload PDF (239K) -
Nobuyuki Aikawa1981 Volume 76 Issue 2 Pages 61-67
Published: February 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe olivines with remarkably well-developed parting, (100), (010) and (001), from the Komori ultrabasic mass along the Maizuru structural belt were investigated by the powder and single-crystal X-ray methods and the optical microscopy. It has become clear that the very strong intensity of 020 reflection on the powder diffraction patterns is not caused by the change of crystal structure, but by the preferred lattice orientation. Dislocation arrays on (100), (010) and (001) in olivines which were heated at 800°C in air were observed under the optical microscope. The partings are closely related with dislocation arrays; the partings have been formed along the planes with dislocation arrays, because those planes have become weak against the mechanical force in relation to structural movement. The alteration after the formation of partings have taken place under the condition of relatively high temperature and low pressure.View full abstractDownload PDF (3540K)
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