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| index | Vol. 49 | 1 | 2/3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | Japanese Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Provenance of Cretaceous and Paleogene sediments in the Median Zone of Southwest Japan
Yoji TERAOKA(Overseas Geology Section, GSJ), Morihisa SUZUKI(Earth Science Laboratory, Faculty of School Education, Hiroshima University) and Kumi KAWAKAMI(Hiroshima Seminary High School)
1998
vol. 49 (8) P. 395-411
16 figs., 1 table
Abstract: The Median Zone of Southwest Japan began to subside rapidly in the mid Cretaceous, and the Goshonoura-Onogawa basin was formed in Late Albian to Santonian time along the Usuki-Yatsushiro Tectonic Line in Kyushu. The succeeding Izumi basin existed in Campanian to Maastrichtian time along the Median Tectonic Line in Shikoku and eastward. In west Kyushu another Late Cretaceous basin called the Himenoura basin appeared in the Coniacian on the north of the Goshonoura-Onogawa basin. These basins were filled with marine and partly nonmarine sediments rich in turbidite, which were supplied mostly from the north and were unconformablly covered by the Paleogene. Petrographical study of sandstones and conglomerates indicates that the Cretaceous and Paleogene sediments consist mainly of clastics of felsic to intermediate volcanic and granitic rocks with minor amounts of those of sedimentary and metamorphic rocks. The sandstones contain detrital garnets derived from various kinds of metamorphic and granitic rocks not only in the Japanese Islands but also in the Asian continent. In this connection some discussions have been made on the classification of garnets in relation to their origin and the boundary between the Sino-Korean and Yangtze Massifs.
@It can be pointed out from the above that the main source area for the Cretaceous and Paleogene sediments was spread over from the Inner Zone of Southwest Japan to the eastern part of the Asian continent.
Distributions of temperature and anion concentrations in stream-sources in Niseko geothermal field, Hokkaido, Japan
Masayori KAWAMURA(Geophsics Department, GSJ)
1998
vol. 49 (8) P. 413-424
6 figs., 3 tables
Keywords: Niseko, geothermal field, spring, river, ground temperature, water temperature, elevation, anion concentration, SO4--
Abstract: Niseko is a geothermal-field located in south-west Hokkaido. Around this field, two large rivers, the Horikabu and Shiribetsu Rivers, flow toward Japan Sea. To these rivers, about 60 small rivers flow down from the mountain area. In 1965,at the source of these small rivers, water temperature and flow rate were measured. And, the concentrations of major anions were also analyzed. On the basis of distributions of these parameters, Niseko area is divided into three sections. In the sect-ions A and C, waters have low in concentration of major anions and relatively high temperature, influenced by difference of the source area elevation.The water in the section B has relatively high concentration of the anions, caused by mixing of hot-spring water. The latter shows high temperature in north-eastern side but low temperature in south-western side. Such phenomena are considered to be caused by difference of mixing, either by hot-spring water or cold mineral water.
Study on water quality as a result of water-rock interaction. -a case study in Fukushima and Ibaraki Prefecture-
Yutaka KANAI(Geochemistry Department, GSJ), Yoji SEKI(Mineral and Fuel Resources Department, GSJ), Hikari KAMIOKA(Geochemistry Department, GSJ), Yasuo KANAZAWA(Mineral and Fuel Resources Department, GSJ), Katsuhiro TSUKIMURA(Mineral and Fuel Resources Department, GSJ), Satoshi HAMASAKI(Mineral and Fuel Resources Department, GSJ) and Terumasa NAKAJIMA(Mineral and Fuel Resources Department, GSJ)
1998
vol. 49 (8) P. 425-438
13 figs., 3 tables
Keywords: water geochemistry, water-rock interaction, spring, surface water, Fukushima, Ibaraki
Abstract: To understand the water-rock interaction and the relationship between geology and water quality, we have studied the spring and surface waters in Fukushima and Ibaraki Prefectures. The amount of total ion equivalent was linear with conductivity, which allows us to estimate the amount of dissolved materials from conductivity. The water quality was influenced by not only geology but also water temperature and standing time. The water quality from granitic area belongs to calcium cabonate-sodium carbonate type, and then increased in alkalinity and alkali ions with standing time. On the other hand, the composition of water from pyroclastic materials showed the tendency of alkali earth metal>alkali metal ions. In this study, we tried a new sampling method to collect the percolated water near the top of mountains. The water collected in this way is surface and shallow water, and contains little dissolved material. These data have been rarely reported although they are important to study the evolution of groundwater.
Mineralogical characteristics of feldspars of the granitoids in Bayankhongor area, central Mongolia
Yuhei Takahashi(IGMR Project, Bureau of Geological Investigation), Sambuu Oyungerel(IGMR Project, Bureau of Geological Investigation), Kazuki Naito(Mineral and Fuel Resources Department, GSJ) and Baljinnyamiin Delgertsogt(MCS International Co.Ltd.)
1998
vol. 49 (8) P. 439-446
4figs., 1table
Keywords: plagioclase, K-feldspar, C-twinning, optic axial angle, granitoids, Mongolia
Abstract: Feldspars of the granitoids in Bayankhongor area, central Mongolia, were investigated mainly by optical methods. The granitoids in this area are classified into dioritic facies (diorite-granodiorite) and granitic facies (granite in a narrow sense). The optic axial angle of K-feldspar of the rocks of the granitic facies decreases in younger rocks, from Riphean to late Paleozoic, but shows the largest value in Mesozoic. This means that the ordering degree of K-feldspar decreased in the order Riphean, early Paleozoic and late Paleozoic. The highest ordered K-feldspar appears in Mesozoic granites.
@In dioritic facies, the frequency of C-twinning of plagioclase increases in order of Riphean (3%), early Paleozoic (22-30%) and late Paleozoic (42-64%). In granitic facies, the frequency of C-twinning is 3% in Riphean, 7% in early Paleozoic, 6 to 65% in late Paleozoic and 4% in Mesozoic.
@Thus the frequency increase of plagioclase C-twinning corresponds to decrease of optical axial angle of K-feldspar. It can be inferred that less frequency of the C-twinning in older granitoids may have resulted from later thermal metamorphic effect.
