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Volume 68, Issue 6
Displaying 1-5 of 5 articles from this issue
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MITSUO HASHIMOTO1973 Volume 68 Issue 6 Pages 177-182
Published: June 05, 1973
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSAmphiboles of basic schists from the Nichinan-cho district, Tottori Prefecture, southwest Japan, are typical barroisites in their chemical and optical characteristics. Ca for 23 oxygen is 1.168 and 1.188 in the two analysed minerals, while AlIV is 1.133 and 1.257, and Na+K in A is 0.139 and 0.172, respectively. The analyses of the host rocks are also given.View full abstractDownload PDF (210K) -
Ken-ichiro Aoki, Yumiko Karashima1973 Volume 68 Issue 6 Pages 183-188
Published: June 05, 1973
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe Otaki dolerite sill, which is about 30 m thick and well-differentiated sill, intruded into the Otaki formation, northern margin of the Shinjo basin, northeastern Japan in the Miocene age. After the intrusion, a magma having about 25 per cent of plagioclase and small amounts of augite and olivine phenocrysts and about 75 per cent of liquid formed many segregation veins (up to 40cm thick) parallel to the contact by fractionation in situ.
The compositions of dolerites and segregation veins vary widely with fractionation, showing the clear increase of SiO2, total FeO, Na2O and K2O and the decrease of Al2O3, CaO and MgO. The trends of the crystallization of the Otaki dolerite magma follow those of high-alumina basalt series of olivine-tholeiite series.
Petrographically and chemically, there were essentially not the three basalt zones, but the high-alumina basalt zone only asociating with tremendous amounts of calc-alkaline andesites and dacites in northeastern Japan during the lower Miocene to upper Pliocene time. Local alkali basalt and tholeiite were of rare exception. Lateral distributions of the tholeiite, high-alumina basalt and alkali basalt zones crossing the Pacific to Japan Sea side would be established at the early Pleistocene time.View full abstractDownload PDF (285K) -
Osamu Ujike1973 Volume 68 Issue 6 Pages 189-198
Published: June 05, 1973
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSHypersthene andesite, erupted on one of the volcanic centers of the Setouchi Petrographic Province, has been studied petrologically. This rock is shown as the typical calcalkaline andesite by the microscopic observations and the chemical analyses. The phenocrysts are composed of an abundance of labradorite, hypersthene, and augite, a small amount of hornblende and ore minerals. Relic of olivine, surrounded by a thick reaction rim of hypersthene, can be found in thin sections of the SiO2-poor variety sometimes. Orthopyroxene phenocrysts (En61.3-66.3) are hypersthenic in a narrow sense, and are clearly different from those (En73.5-89.1) of the phenocryst-poor andesites (Ujike, 1972) from the same area.
Parallel-growth of hypersthene (inside) and augite (outside), which has been considered as a phenomenon caused by magmatic contamination process (Ota, 1958), appears in this andesite. The data obtained by high temperature melting experiments of natural rock compositions have been compiled from literature to show that magmatic chemistry, especially normative Wo/(Wo+En+Fs), would strongly control the order of crystallization of the two pyroxenes. In short, from melt being 100×Wo (Wo+En+Fs)_??_20 by weight, ortho- and clinopyroxenes have likely been to start crystallization simultaneously; from melt having the value smaller than 15, orthopyroxene has crystallized at a higher temperature than clinopyroxene very often. This compilation suggests that the augite must have nucleated at a slightly lower temperature than the hypersthene on the surface of the latter crystal from the hypersthene andesitic magma having low Wo component, and that no contamination process might be needed to explain the parallel-growth of the pyroxenes. This kind of parallel-growth may be found frequently in calc alkaline andesite since Wo content of average andesite is small.View full abstractDownload PDF (526K) -
Akihiko Okada, Takuya Okada, Makoto Shima1973 Volume 68 Issue 6 Pages 199-203
Published: June 05, 1973
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSMagnetic property and Fe57 Mossbauer effect are studied on the iron-manganese oxide phase of the Pacific Ocean manganese nodules. The results show that the iron-manganese oxide phase is composed of fine-grained particles. The phase shows a super-paramagnetic property from about 40°K to room temperature, and magnetic ordering is observed at the lower temperature. The isomer shifts calculated from the Mossbauer spectra show that the iron in the iron-manganese oxide phase is in the ferric state.View full abstractDownload PDF (209K) -
Keiichi Omori1973 Volume 68 Issue 6 Pages 204-209
Published: June 05, 1973
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSDownload PDF (208K)
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