巻号一覧
25 巻 (1991)
- 6 号 p. 411-
- 5 号 p. 357-
- 4 号 p. 199-
- 3 号 p. 137-
- 2 号 p. 57-
- 1 号 p. 1-
25 巻, 5 号
選択された号の論文の4件中1～4を表示しています
- |<
- <
- 1
- >
- >|
-
Kazuhiro Suzuki, Mamoru Adachi1991 年 25 巻 5 号 p. 357-376
発行日: 1991年
公開日: 2008/04/08
ジャーナル フリーPrecise electron microprobe analysis makes it possible to determine the Th, U and Pb concentrations in an area less than 5 μm across in a single grain of monazite, zircon or xenotime; the detection limit of PbO at 2σ confidence level is 0.005–0.008 wt.% and the relative error is 3% for 0.2 wt.% concentration level. The subgrain analyses of monazite are plotted on the coordinates of PbO and ThO2* (ThO2 plus the equivalent of UO2), and those of zircon and xenotime on the coordinates of PbO and UO2* (UO2 plus the equivalent of ThO2). Data points are arrayed linearly and enable us to define an isochron which passes through the origin. The chemical Th-U-total Pb isochron ages coincide well with mineral and whole-rock ages isotopically determined for the same samples. The chemical Th-U-total Pb isochron method was applied to the age determination of monazite, zircon and xenotime from the Tsubonosawa paragneiss and the host Hikami granite in the South Kitakami terrane of Northeast Japan. The chemical ages show that (1) the sedimentation of the gneiss-protolith occurred soon after the emplacement of 500 Ma granitoids in the source region, where the 500 Ma granitoids were widespread together with Precambrian rocks possibly dated back to as old as Archean (3080 ± 180 Ma), (2) the gneiss-protolith was metamorphosed to the amphibolite facies grade about 430 ± 10 Ma ago, and (3) the gneiss was affected by multiple thermal events of 350, 260, 180 and 100 Ma. The 350 Ma event corresponds to the intrusion of the Hikami granite, and the 100 Ma one to the intrusion of the Cretaceous Kesengawa granite. The 260 and 180 Ma events may correspond in age to the main metamorphic event and subsequent igneous activity in the Hida terrane, central Japan. The chemical Th-U-total Pb isochron age in terms of the precise microprobe analysis of low-level Th, U and Pb will open a new vista on the Paleozoic-Mesozoic tectonics of the Japanese Islands.抄録全体を表示PDF形式でダウンロード (4782K) -
Takao Oi, Junpei Kato, Tomoko Ossaka, Hidetake Kakihana1991 年 25 巻 5 号 p. 377-385
発行日: 1991年
公開日: 2008/04/08
ジャーナル フリーA series of experiments was carried out in which boron minerals were precipitated from pH- and chemical composition-controlled solutions at 25°C and boron isotope fractionation accompanying the mineral deposition was measured. Borax, sassolite and sborgite were synthesized from aqueous boric acid-sodium hydroxide solutions. Borax was obtained from solutions with higher pH and sassolite from solutions with lower pH, irrespective of the mole ratio of B and Na in the solution. The fractionation factor, S, defined as S = (11B/10B)mineral/(11B/10B)solution increases with increasing the pH of the solution for both borax and sassolite. A cross-over point at which S = 1 was found at about pH = 9.5 for borax, while S was always larger than unity for sassolite. The present results of boron isotope fractionation are consistent with theoretical prediction of equilibrium isotope effects, although the experimental equilibrium constant of the boron isotope exchange reaction between B(OH)3 and B(OH)4– at 25°C is larger than that theoretically predicted (1.03–1.05 compared to 1.0194).抄録全体を表示PDF形式でダウンロード (2546K) -
Ming Zhang, Martin A. Menzies, Paul Suddaby, Matthew F. Thirlwall1991 年 25 巻 5 号 p. 387-398
発行日: 1991年
公開日: 2008/04/08
ジャーナル フリーCombined geological and geochemical evidence suggests that the age of the basement through which the Wudalianchi, Erkeshan, and Keluo (WEK) volcanic rocks in NE China were erupted is post-Archaean. Sr, Nd, and Pb isotope analyses demonstrate that the Miocene to Recent WEK potassic volcanic rocks were derived from an enriched mantle source which had been metasomatised during the Proterozoic. The primary potassic magmas are the products of partial melting of either this enriched mantle source or, more probably, a mixture of this enriched source with an OIB source. In either case, a post-Archaean subcontinental lithospheric mantle with an EM1 signature has made a significant contribution to the WEK potassic rocks.抄録全体を表示PDF形式でダウンロード (3015K) -
Pradeep Kumar, P. S. Goel1991 年 25 巻 5 号 p. 399-409
発行日: 1991年
公開日: 2008/04/08
ジャーナル フリーMany samples of bulk and sieved fractions of Ambapur Nagla and other stone meteorites as well as acid insoluble residues of Sikhote Alin iron meteorite have shown isotopically anomalous ratios for 190Os/184Os as measured by RNA. Both positive and negative deviations, relative to terrestrial standard, are seen. The largest values, found in bulk samples are 60% enrichment of 190Os in Efremovka and 50% depletion in Allende. The number of anomalous cases are very few (19–22%) as compared to the normal cases. Apparently isotopically anomalous osmium is contributed from interstellar or extraneous matter in both stone and iron meteorites.抄録全体を表示PDF形式でダウンロード (2518K)
- |<
- <
- 1
- >
- >|