BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 61 , Issue 11-12
Showing 1-8 articles out of 8 articles from the selected issue
Article
  • Shunso Ishihara, Chappell Bruce W
    2010 Volume 61 Issue 11-12 Pages 383-415
    Published: December 22, 2010
    Released: July 09, 2013
    JOURNALS FREE ACCESS
        Granitoids from porphyry copper mineralized regions from selected areas in the world were reexamined by the polarized X-ray method. The studied samples in Chile include regional collection of three transects, North, Central and South, including Chuquicamata, El Salvador, Rio Blanco-Los Blances and El Teniente mines. The east-west variation in younging the age toward east is best shown in the North and Central transects. Components that tend to increase toward the inner direction are Al2O3,Na2O, P2O5 and Sr, while those of decreasing are Y, total Fe and V. The innermost is a zone of porphyry copper deposits. Therefore, high Sr/Y granitoids prevail in the innermost and youngest zone.
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  • Yukio Yanagisawa, Hironori Hiranaka, Katsuki Kurokawa
    2010 Volume 61 Issue 11-12 Pages 417-443
    Published: December 22, 2010
    Released: July 09, 2013
    JOURNALS FREE ACCESS
        The Miocene diatom biostratigraphy has been established for the Nomura and Tokonami Formations in the Tsugawa area, Niigata Prefecture, Japan. The Nomura Formation is composed of massive diatomaceous mudstone intercalating numerous tephra beds. The Tokonami Formation consists of the lower sandy mudstone with ne to medium-grained sandstone beds, and the upper very ne to ne-grained sandstone and cross-bedded coarse-grained sandstone. The Nomura Formation is correlative with Neogene North Paci c diatom zones NPD5B through NPD7A, and estimated ca 13 Ma to 6.4 Ma in age. In the lower to middle part of the Tokonami Formation, the latest Miocene diatom subzone NPD7Ba is recognized. The upper part of the formation is not datable because of the paucity of age-diagnostic diatoms, but the top of the Tokonami Formation may be below the Miocene/ Pliocene boundary. The Nomura and Tokonami formations are correlated to the Teradomari Stage.
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  • Takayuki Uchino, Makoto Kawamura
    2010 Volume 61 Issue 11-12 Pages 445-452
    Published: December 22, 2010
    Released: July 09, 2013
    JOURNALS FREE ACCESS
        Glaucophane was obtained from meta-basalt in the Nedamo Complex (Early Carboniferous accretionary complex) of the Nedamo Terrane, Northeast Japan. The meta-basalt proved to have undergone high-pressure type metamorphism of the epidote-blueschist subfacies from the mineral assemblage of glaucophane, epidote and quartz. Although the 380 Ma Tateishi Schists, which underwent high-pressure type metamorphism, had been already reported from a tectonic zone in the Nedamo Terrane, it is considered to be not the Nedamo Complex-proper but the pre-Carboniferous tectonic block displaced there by a tectonic movement. Judging from the occurrence, weak deformation and recrystallization of the meta-basalt, it is considered to be a member of the Nedamo Complex-proper. Then a part of the Nedamo Complex proved to have undergone high-pressure type metamorphism.
        There is the interpretation that the Nedamo Complex might correlate with the high-P/T Motai Metamorphics on the basis of their lithologic similarity. The evidence of the high-pressure type metamorphism in the Nedamo Complex is consistent with such interpretation.
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  • Susumu Tanabe, Rei Nakashima, Hideyoshi Yoshioka, Mio Takeuchi, Yasuyu ...
    2010 Volume 61 Issue 11-12 Pages 453-463
    Published: December 22, 2010
    Released: July 09, 2013
    JOURNALS FREE ACCESS
        The GS-AHH-1 core, obtained from the buried terrace under Adachi-ku in the Tokyo Lowland, consists of facies BR (braided river sediments), TM (tide-influenced shallow marine sediments), TF (tidal fl at sediments), SM (shallow marine sediments), PD-DF (prodelta to deltafront sediments), MT (modern tidal fl at sediments) and AS (artifi cial soil) in ascending order. The Alluvium (latest Pleistocene to Holocene incised valley fi lls), which consists of facies TF, SM, PD-DF, MT and AS, unconformably overlie Shimosa Group (middle to late Pleistocene deposits) of facies BR and TM. The facies TF and SM and facies PD-DF, MT and AS can be correlated to estuary and delta systems, respectively. The Maximum Flooding Surface at the estuary-delta system boundary is dated at 6.9-7.3 cal kyr BP. The facies TF, which consists of bluish gray mud, overlies the facies TM, which consists of greenish gray mud, with sharp boundary. The difference in the color of mud can be a good indicator to identify the Shimosa Group–Alluvium boundary in this region.
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Report
  • Kentaro Sakata, Tsutomu Nakazawa
    2010 Volume 61 Issue 11-12 Pages 465-475
    Published: December 22, 2010
    Released: July 09, 2013
    JOURNALS FREE ACCESS
        Petrographic properties of 12 layers of Late Pleistocene tephra which can be observed at the southeastern foot of the Akagi Volcano, Gunma Prefecture, central Japan are described. Detailed examination of these tephra layers reveals that Ag-Nm2, Ag-UP, Ag-KP tephras comprise a few fall units representing different refractive indices of orthopyroxene and hornblende crystal grains from each other. Furthermore, Ag-MzP3, Ag-MzP2, Ag-Nm2, and Ag-UP tephras represent largely different refractive indices from the property of the majority of the examined tephras. These petrographic features are important for identifi cation and correlation of these tephra layers.
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  • Takashi Kudo
    2010 Volume 61 Issue 11-12 Pages 477-484
    Published: December 22, 2010
    Released: July 09, 2013
    JOURNALS FREE ACCESS
        The formation age of Mikadoishi Lava Dome at Towada volcano was estimated based on the petrological features of eruptive rocks during the post-caldera stage in Towada volcano. The lava dome has dacite compositions (66.4 wt.% SiO2) and contains plagioclase, clinopyroxene, orthopyroxene and Fe-Ti oxide phenocrysts. The petrological features show that the lava dome does not correlate with any tephras from the post-caldera stage. This indicates that the lava dome eruption was not accompanied with notable pyroclastic eruptions. The formation age of the Mikadoishi Lava Dome can be estimated to be sometime within 11.7-2.7 cal kyr BP on the basis of the temporal change of magma compositions in the post-caldera stage.
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Short Article
  • Shunso Ishihara, Tuan Anh Tran, Kezhang Qin
    2010 Volume 61 Issue 11-12 Pages 485-488
    Published: December 22, 2010
    Released: July 09, 2013
    JOURNALS FREE ACCESS
        Sulfur isotopic ratios were studied on representative lead-zinc feeding ores, zinc concentrates and lead concentrates from selected mines in North Vietnam. These sulfi des from the Triassic rhyolite hosted ore deposits have δ34S values of +3.4 to +4.7 ‰, while those from purely Paleozoic sedimentary host rocks are slightly heavier, ranging from +4.4 to +8.2 ‰. No δ34S values similar to those of the Mississippi Valley-type lead-zinc ores have been found. Lead concentrates are always smaller than zinc concentrates in the δ34S values. Two very depleted δ34S values were found in the Cho Dien mine area where detailed isotopic study is necessary.
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