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Volume 72, Issue 6
Displaying 1-6 of 6 articles from this issue
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Evidence for Melting in the Wet Archean MantleEiji OHTANI, Kenji MIBE, Takumi KATO1996 Volume 72 Issue 6 Pages 113-117
Published: 1996
Released on J-STAGE: October 17, 2006
JOURNAL FREE ACCESSWe have conducted melting experiments of pyrolite containing 1 and 2wt.% of water at 6.5GPa by a multianvil high pressure apparatus. We observed melting at temperatures above 1550°C and 1700°C for pyrolite+2%H2O and pyrolite+1%H2O respectively at 6.5GPa. A small amount of water reduces the solidus temperature by 250-100°C. Another important observation is expansion of the stability field of orthopyroxene above the solidus, and reduction of the stability field of olivine+liquid. The present observation of expansion of the orthopyroxene stability field above the solidus at 6.5GPa implies that the harzburgite residue can be formed by partial melting of the primitive mantle under the hydrous conditions at the depth of around 200km. Hydrous melting is a key process to fill the missing link between the cratonic peridotite and komatiite; i.e., cratonic peridotite was formed as a residue of the komatiite extraction in a wet Archean mantle.View full abstractDownload PDF (574K) -
Upper Mantle Material Exposed in an Extinct Back-arc BasinYasuhiko OHARA, Shigeru KASUGA, Teruaki ISHII1996 Volume 72 Issue 6 Pages 118-123
Published: 1996
Released on J-STAGE: October 17, 2006
JOURNAL FREE ACCESSSerpentinized peridotites and gabbros were dredged from the axial zone of the Parece Vela Basin during a cruise of S/V Takuyo in 1995. The central zone of the Parece Vela Basin is characterized by the NS trending chain of depressions forming right-step en-echelon alignment. Our petrological studies suggest that the peridotites are residues of extensive partial melting of primitive mantle peridotites. Presence of hydrous phases in the peridotites indicates that the peridotites were subjected to metasomatic event in the upper mantle beneath the Parece Vela Rift.View full abstractDownload PDF (3156K) -
Izumi YOKOYAMA1996 Volume 72 Issue 6 Pages 124-128
Published: 1996
Released on J-STAGE: October 17, 2006
JOURNAL FREE ACCESSDeformations around volcanoes have been detected by geodetic methods since the beginning of the 20th century, especially in Japan. Generally speaking, the deformations are usually expanding or contracting due to magmatic pressure and are simple compared with the crustal deformations accompanied by earthquakes. Co-eruptive deformations are interpretable by various elastic models which are defined mainly by types of the pressure sources, their depths and pressure increments. It is not always easy to discuss pre- and post-eruptive deformations because we need accumulation of observational results of precise geodetic surveys on and around volcanoes for a long term. The author found just appropriate examples in the 1914 and 1946 eruptions of Sakurajima volcano and in the 1983 eruption of Miyakejima volcano. By use of the data, the author shows that post-eruptive deformations of the two volcanoes are interpreted by rheological recovery of the medium beneath the volcanoes. On the assumption that the recovery stages can be approximated by the Kelvin models, the viscosities of the upper crust in these areas are estimated at 1019Pa•s in order of magnitude. The value is nearly the same as the viscosity of granite beams obtained through the laboratory experiments for more than 30 years by N. Kumagai and his group.View full abstractDownload PDF (672K) -
Hiroki SATO, Kenichi MURO, Akira HASEGAWA, Ko HASHIZUME1996 Volume 72 Issue 6 Pages 129-132
Published: 1996
Released on J-STAGE: October 17, 2006
JOURNAL FREE ACCESSDistribution of partial melt (magma) in the upper mantle is investigated in detail from the seismic tomography of the mantle wedge beneath northeastern Japan. The comparison of the fine velocity structure with the laboratory velocity data on a partiall-ymolten mantle rock yields estimates of three-dimensional distribution of melt. The results indicate that the cause of island arc volcanism in northeastern Japan is the upwelling of hot mantle materials (volcanic plumes) from beneath. The source of volcanic magma is diapir-like melting regions localized within the volcanic plumes. Extensive volcanic activity at the volcanic front is due to the presence of the vast melting zones right beneath the Moho discontinuity. Those melting zones may cause melting of lower crustal materials and produce felsic magma. Melt stays underneath the Moho, where crystallization fractionation may proceed. Melt exists at greater depths in the back-arc region, which may cause across-arc variations of chemical compositions of the volcanic rocks in northeastern Japan. We suggest that magma migration in the ductile lower crust may cause low-frequency microearthquakes, and magma penetration into the brittle upper crust may produce mid-crustal S-wave reflectors.View full abstractDownload PDF (2377K) -
Shuji MATSUZAWA, Tetsuya TANIGAMI, Qi WANG1996 Volume 72 Issue 6 Pages 133-136
Published: 1996
Released on J-STAGE: October 17, 2006
JOURNAL FREE ACCESSDrawn poly(vinyl trifluoroacetate) (PVTFA) films were converted into syndiotacticity-rich poly(vinyl alcohol) (s-PVA) films through the saponification in solid state with gaseous ammonia. The intensities of crystallization and racemic dial sensitive bands in infrared absorption spectra of the s-PVA films decreased with increasing heat-drawing ratio before Saponification. In the s-PVA film prepared from the PVTFA heat drawn before saponification, the intensity of crystallization sensitive band did not change whereas that of racemic dial sensitive band decreased with heating time respectively. This means that the solid s-PVA prepared from heat-drawn PVTFA has the solid structure determined by that of PVTFA, i. e. the low degree of crystallization and high hydrogen bond content. The s-PVA has hot-water resistance and only soluble at temperatures above 100°C.View full abstractDownload PDF (1629K) -
Michi-hiko OGATA1996 Volume 72 Issue 6 Pages 137-141
Published: 1996
Released on J-STAGE: October 17, 2006
JOURNAL FREE ACCESSAs indicated by the experiment in early days (Ogata, 1965), the electrical resistance of the myoplasm in resting state is very high compared with that in activated state. This is in accord with the observation that water is only slowly squeezed out from relaxed muscle fragments by applying pressure, compared with that from the activated muscle fragments. All these findings suggest that the water in the relaxed fiber is well retained by structural proteins in accord with the structure of water in resting muscle demonstrated by 1H-NMR studies.View full abstractDownload PDF (702K)
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