巻号一覧
15 巻 (1981)
- 6 号 p. 295-
- 5 号 p. 229-
- 4 号 p. 163-
- 3 号 p. 109-
- 2 号 p. 51-
- 1 号 p. 1-
15 巻, 3 号
選択された号の論文の3件中1～3を表示しています
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R. J. Arculus, R. W. Johnson1981 年 15 巻 3 号 p. 109-133
発行日: 1981/06/20
公開日: 2008/04/08
ジャーナル フリーEnrichments in Sr, Ba, and Pb relative to the light rare-earth elements in island-arc basalts have been taken as evidence for the involvement of subducted, upper-crust-derived sediments, or altered oceanic crust, or sea-water, in the upper-mantle source regions of primary island-arc magmas. However, the Sr enrichments are unlikely to have been caused by addition of these 87Sr-rich materials, because there is no positive correlation between the magnitude of the Sr anomalies and 87Sr/86Sr values in most island-arc rock suites. On the contrary, these parameters in some arcs are negatively correlated. Furthermore, Sr, Ba, and Pb anomalies are found in non-island-arc rocks, such as those from continental-flood lava sequences and other areas where subduction is unlikely to have taken place; and Sr and Nd isotopic data for both non-arc and island-arc rocks plot in similar parts of εNd-versus-εSr diagrams. These relationships, as well as the absence of marked Th and U enrichments in island-arc basalts, are generally consistent with primitive island-arc magmas having been contaminated by 87Rb-poor (low 87Sr/86Sr) lower crust. Contamination by crust in the island-arcs themselves may be a more important process than addition of subducted material to the mantle wedge above downgoing slabs.抄録全体を表示PDF形式でダウンロード (7878K) -
Lead isotope measurements on ores, igneous and sedimentary rocks from the kuroko mineralization areaKazuo Sato, Maryse H. Delevaux, Bruce R. Doe1981 年 15 巻 3 号 p. 135-140
発行日: 1981/06/20
公開日: 2008/04/08
ジャーナル フリーLead isotope ratios are measured for five ores, five Paleozoic sedimentary rocks, and six Miocene igneous rocks from the Hokuroku Basin, northern Honshu, to see if any genetic link exists between the kuroko mineralization and its immediate basement. The ore lead data show no significant variation and are within analytical uncertainties of the previous analyses of kuroko deposits from northeast Japan. The rock lead data have a large spread relative to the data available for kuroko deposits from northeast Japan. Certain Paleozoic sediments, which are thought to be the most representative of the basement underlying the mineralization, are significantly more radiogenic than the kuroko ores. The data for igneous rocks, on the other hand, fall in a narrow range, though their rock type ranges from mafic to fairly felsic in composition, and are all similar to the available kuroko ore data. The kuroko lead, therefore, is likely to come mainly from the igneous rocks rather than from the immediate basement, although some lead contribution from the basement rocks is also suggested.抄録全体を表示PDF形式でダウンロード (1564K) -
V. J. Dietrich, A. Gansser, J. Sommerauer, W. E. Cameron1981 年 15 巻 3 号 p. 141-161
発行日: 1981/06/20
公開日: 2008/04/08
ジャーナル フリーGorgona island is the only place in the world where young ultramafic (pyroxenitic) komatiitic lava flows are known to occur. The island, which appears to be a small southern remnant of the Colombian Coastal Cordillera, is built up of serpentinised peridotites, gabbros, basalts and associated Palaeogene oceanic sediments. Spinifex texured rocks occur within the basaltic and doleritic complex, closely associated with pillow basalts of tholeiitic composition. During rapid cooling the order of crystallisation was: olivine (Fo90-91), high Al-calcic pyroxene and Cr-spinel as the major quenched phases; then olivine (Fo86-82). low Al-calcic pyroxene, plagioclase (An75-81) and Ti-magnetite as quenched products in the interstitial groundmass. Bulk chemistry: MgO ∼ 16wt.% (Mg/Mg+Fe2+ = .74), Cr ∼ 1250ppm, Ni ∼ 700ppm, Sc ∼ 33ppm, Ba ∼ 5 ppm, Zr ∼ 30 ppm, Y ∼ 15 ppm; flat REE pattern (5 to 8 x chondrites) with slight depletion of LREE. The associated basalts and dolerites yield similar pattern, although slightly enriched in LREE. Model calculations incorporating major and trace elements show that fractionation of 20-25% olivine + 0.5% Cr-spinel from the komatiitic liquid could produce olivine tholeiites similar to those of Palaeogene Nazca plate. The unique structural setting of the Gorgona rocks probably results from a rapid uplift of a central part of the Nazca ridge including immature magma chambers.抄録全体を表示PDF形式でダウンロード (6646K)
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