BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 59 , Issue 3-4
Showing 1-5 articles out of 5 articles from the selected issue
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  • Susumu Tanabe, Yoshiro Ishihara, Rei Nakashima, Katsumi Kimura, Toshio ...
    2008 Volume 59 Issue 3-4 Pages 135-149
    Published: November 20, 2008
    Released: August 28, 2013
    JOURNALS FREE ACCESS
        We examined time and spatial distributions of sedimentary facies surrounding the spit sediments in the bay-mouth portion of the Paleo-Okutokyo Bay by using sedimentary facies and radiocarbon dates obtained from two sediment cores (MZ and SZ cores) from the eastern margin of the Tokyo Lowland. Latest Pleistocene to Holocene incised-valley fills (the Chuseki-so) which unconformably overlie Middle to Late Pleistocene deposits Shimosa Group) consist of braided river, meandering river, estuary, spit and delta sediments in MZ core in ascending order. The Chuseki-so consists of delta sediments in SZ core. MZ and SZ cores yields radiocarbon dates ranging from 13150 to 3160 cal BP and from 3930 to 730 cal BP, respectively. Sand shoal sediments constituting part of the spit sediments in MZ core forms a sand body which elongates northeastward from the spit sediments. nd this sand body seems to have deposited in a bay-mouth channel which existed behind the spit between 4500 nd 3500 cal BP.
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  • Shunso Ishihara, Bruse W. Chappell
    2008 Volume 59 Issue 3-4 Pages 151-170
    Published: November 20, 2008
    Released: August 28, 2013
    JOURNALS FREE ACCESS
        Late Cretaceous granitoids of central area in the Abukuma terrain were analyzed by polarized XRF method and compared with the Ryoke granitoids of Chubu district. The Abukuma granitoids are mostly composed of hornblende and/or biotite granodiorite to granite and less in amount of muscovite-biotite granites, and are higher in Na2O and Al2O3, lower in K2O, Rb, Pb and Ba than the Ryoke granitoids on the Harker diagrams. The Abukuma granitoids appear to be generated within the continental crust of inmatured island-arcs, having mafic magmas and heat from the upper mantle. The Abukuma granitoids are generally reduced type accepting sedimentary carbon from the continental crust, similarly to the Ryoke granitoids, but an intermediate series occurs in the eastern-end zone. Zone II granitoids, which are rich in CaO and poor in K2O and lithophile components such as Rb, Pb, Y, Ce and La, have weak signature of high Sr/Y ratio for adakite. An adakitic magma may have brought up from the subducting slab, but extremely modified within the continental crust.
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