Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
29 巻 , 6 号
  • Yasutaka Terakado, Waitsu Nakajima
    1995 年 29 巻 6 号 p. 337-345
    発行日: 1995/12/20
    公開日: 2008/04/08
    ジャーナル フリー
    Abundances of rare earth elements (REE), Ba, Sr and Rb were determined for several kinds of zeolites occurred in cavities of volcanic rocks from Japan with relevance to peculiar crystal chemical properties of zeolites. Because of the scarcity of REE data of zeolites, the following points would be noteworthy: (1) REE abundances for those zeolites are extremely low, ranging from about 0.01 to 0.1 in chondrite normalized unit; (2) Mutual fractionation among REE is rather small aside from small Eu and Ce anomalies; (3) Three different zeolite species from Maze area, Niigata Prefecture, show considerable resemblance with respect to REE, Ba and Sr concentrations. It is suggested that the REE incorporation in zeolites seems to be affected by their genetic process or formation environment rather than by difference in zeolite species. Moreover, relatively low REE abundances in zeolites may reflect extremely low REE abundances in the solutions from which those zeolites were precipitated. The Ce anomalies for the Maze samples show that those zeolites have not been deposited from magmatic solutions but from meteoric water.
  • Masayo Minami, Hiroshi Shimizu, Akimasa Masuda, Mamoru Adachi
    1995 年 29 巻 6 号 p. 347-362
    発行日: 1995/12/20
    公開日: 2008/04/08
    ジャーナル フリー
    Isotopic data of Sm-Nd, La-Ce and Rb-Sr systems, rare earth element (REE) abundances and major element compositions are reported for the Archean Marble Bar Chert from the Towers Formation of the Salgash Subgroup, Warrawoona Group, Pilbara Block, Western Australia. The Marble Bar Chert records two Sm-Nd ages; 3.2±0.3 Ga for red (or black) and white banded cherts and 2.5±0.2 Ga for yellowish gray cherts. These ages contain relatively large uncertainties and are younger than 3.45 Ga U-Pb zircon ages previously reported for the Salgash Subgroup. The results imply some later perturbation in Sm-Nd system of these cherts after their formation. However, the older age of 3.2±0.3 Ga is close to the U-Pb zircon ages for the Salgash Subgroup within analytical errors and therefore can be regarded as the formation time of the banded cherts. On the other hand, the younger age of 2.5±0.2 Ga for the yellowish gray cherts is thought to reflect the time of later thermal events and the cherts do not retain their original chemical features. The 3.2 Ga Sm-Nd age for the Marble Bar banded cherts is the first Archean record obtained for the Archean cherts; their initial εNd value of +1.0±3.0 holds the original nature at their formation without severe geochemical disturbance. The obtained mantle-like depleted or chondritic feature at 3.2 Ga for the banded cherts, together with their SiO2 and Fe2O3∗ data and positive Eu anomalies in REE patterns, suggests substantially large contribution of hydrothermal solution derived from depleted- or chondritic-mantle to the cherts and inorganic origin of the cherts, which contrasts to Phanerozoic biogenic cherts.
  • Jong Ik Lee, Hiroo Kagami, Keisuke Nagao
    1995 年 29 巻 6 号 p. 363-376
    発行日: 1995/12/20
    公開日: 2009/02/06
    ジャーナル フリー
    Abstract-Rb-Sr whole rock isochron ages and K-Ar mineral ages have been determined for late Cretaceous granitic rocks distributed in the southern part of the Kyeongsang basin, Korea. The granitic rocks are grouped into seven in four areas (Masan, Jinhae, Kimhae and Busan) based on their petrological features. In the five plutons, Rb-Sr whole rock isochron ages and isotopic initial ratios were determined as follows:
                    Rb-Sr whole rock age    Initial Sr ratio
    Masan Hbbtgr    100.1 ± 7.1 Ma    0.70489 ± 0.00012
    Jinhae Btgr        70.5 ± 1.9 Ma    0.70497 ± 0.00006
    Kimhae Hbbtgr    83.9 ± 9.0 Ma    0.70538 ± 0.00021
    Busan Btgr (YS)    70.6 ± 4.2 Ma    0.70531 ± 0.00029
    Busan Btgr (KP)    68.8 ± 3.4 Ma    0.70579 ± 0.00028
    Rb-Sr whole rock ages become younger toward more felsic and smaller plutons, which is thought to reflect progressive lowering in melting degree at the source with time. Initial Sr ratios of each pluton progressively increase from the western to eastern areas, regardless of their ages. This means that the granitic magmas have been more evolved toward the eastern area due to much contribution from lower crustal materials. K-Ar ages of biotite are about 3 to 15 m.y. younger than Rb-Sr whole rock isochron ages in each plutonic unit. Average cooling rate of each body is directly proportional to the volume of granitic body. The conduction-loss of heat due to large thermal contrast and the circulating meteoric water between a granitic body and the country rock at shallow levels are thought to have directly affected the average cooling rate of each body. Initial Sr isotopic ratios of the granitic rocks in the study area are well correlated with those of the central to northern Kyushu and the North Zone of Southwest Japan. Rb-Sr isochron ages of the Cretaceous granitic rocks became younger from central Kyushu (120-100 Ma) through northern Kyushu (115-90 Ma) to southern part of the Kyeongsang basin (100-70 Ma). The granitic magmatism having 70 Ma ages on the eastern side of the Yangsan Fault is thought to be better correlated with those of the North Zone of Southwest Japan.
  • Yuji Sano, Naoto Takahata, Toshitaka Gamo
    1995 年 29 巻 6 号 p. 377-384
    発行日: 1995/12/20
    公開日: 2008/04/08
    ジャーナル フリー
    We have measured 3He/4He and 4He/20Ne ratios and 4He concentrations in 19 South Pacific water samples with various depths from station SA-6 located in the Solomon Sea (6°38'S, 153°38'E) and SA-7 in the central Coral Sea Basin (14°16'S, 154°19'E) on the KH-92-4 cruise of the Research Vessel, Hakuho Maru of the University of Tokyo. The 3He/4He and 4He/20Ne ratios vary significantly from 0.988 Ratm to 1.276 Ratm and from 0.254 to 0.292, respectively. An extensive plume of water enriched in 3He has been discovered at a depth of about 2000 meter. Taking 3He/4He data of the Geosecs and the South Tow expeditions, 25% excess 3He plume can be traced over 5000 kilometers to the west of the East Pacific Rise. Observed 25% excess 3He plume at SA-6 and 7 may be independent from the ridge, which suggests that there is another source of the mantle derived helium in the area studied.