S. Togashi

Geological Survey of Japan

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N. T. Kita

University of Wisconsin–Madison

Y. Morishita

Geological Survey of Japan

Tsuyoshi Tanaka

Kobe University

Akihiko Tomiya

Geological Survey of Japan

Hikari Kamioka

Geological Survey of Japan

Satoshi Kanisawa

Tohoku University

Noboru Imai

Geological Survey of Japan

Maya Yasui

Nihon University

Shirô Tamanyu

National Institute of Advanced Industrial Science and Technology

N. Miyaji

Nihon University

Cooperative Institutions

Geological Survey of Japan

National Institute of Advanced Industrial Science and Technology

The University of Tokyo

Nagoya University

Czech Academy of Sciences, Institute of Geology

Tohoku University

Japan Advanced Institute of Science and Technology

Hiroshima University

Fukuoka University

Kyushu University

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JNdi-1: a neodymium isotopic reference in consistency with LaJolla neodymium

Chemical Geology (2000)

Tsuyoshi Tanaka S. Togashi Hikari Kamioka Hiroshi Amakawa Hiroo Kagami

Neodymium

Isobaric process

10.1016/s0009-2541(00)00198-4

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Citations (1,625)

Sr variation by fractional crystallization for volcanic rocks from island arcs and continental margins

Chemical Geology (1985)

S. Togashi

Fractional crystallization (geology)

Alkali basalt

Anorthite

Incompatible element

Igneous differentiation

10.1016/0009-2541(85)90086-5

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Citations (2)

Sr isotope geochemistry of voluminous acidic pyroclastics erupted at 1-3Ma in Northeast Japan.

JOURNAL OF MINERALOGY PETROLOGY AND ECONOMIC GEOLOGY (1989)

Teruo Shirahase Shirô Tamanyu S. Togashi

Sr isotope ratios are analyzed for voluminous acidic pyroclastics erupted at 1-3 Ma in five areas on the volcanic front of Northeast Japan. The initial values of 87Sr/86Sr ratios range from 0.7040 to 0.7055. There is no significant difference in ratios between 1-3 Ma acidic pyroclastics and 0-1 Ma andesitic volcanics in each area in spite of differences in age and in mean SiO2 content. On the other hand, the ratios in both of 1-3 Ma and 0-1 Ma volcanics vary along arc in the same manner. The changes of Sr and Rb contents in each area are consistent with systematic changes by fractional crystallization. The low 87Sr/86Sr ratios and chemistry suggest that 1-3 Ma acidic pyroclastics of Northeast Japan formed by a high degree of fractional crystallization from basic magma which is common in genesis with young andesitic volcanism. The mechanisms of the formation of the basic magma and the character of mantle source in each area have not changed for the past 3 Ma. Degrees of fractional crystallization changed with changes of the tectonic condition of shallow magma chamber from a weak horizontal compression stress field to a strong one.

Fractional crystallization (geology)

Isotope Geochemistry

10.2465/ganko.84.200

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Citations (4)

The relative formation ages of ferromagnesian chondrules inferred from their initial aluminum‐26/aluminum‐27 ratios

Meteoritics and Planetary Science (2002)

S. Mostefaoui N. T. Kita S. Togashi Shogo Tachibana H. Nagahara

Abstract— We performed a systematic high‐precision secondary ion mass spectrometry 26 Al‐ 26 Mg isotopic study for 11 ferromagnesian chondrules from the highly unequilibrated ordinary chondrite Bishunpur (LL3.1). The chondrules are porphyritic and contain various amounts of olivine and pyroxene and interstitial plagioclase and/or glass. The chemical compositions of the chondrules vary from FeO‐poor to FeO‐rich. Eight chondrules show resolvable 26 Mg excesses with a maximum δ 26 Mg of ˜1% in two chondrules. The initial 26 Al/ 27 Al ratios inferred for these chondrules range between (2.28 ± 0.73) × 10 −5 to (0.45 ± 0.21) × 10 −5 . Assuming a homogeneous distribution of Al isotopes in the early solar system, this range corresponds to ages relative to CAIs between 0.7 ± 0.2 Ma and 2.4 +0.7 −0.4 Ma. The inferred total span of the chondrule formation ages is at least 1 Ma, which is too long to form chondrules by the X‐wind. The initial 26 Al/27Al ratios of the chondrules are found to correlate with the proportion of olivine to pyroxene suggesting that olivine‐rich chondrules formed earlier than pyroxene‐rich chondrules. Though we do not have a completely satisfactory explanation of this correlation we tentatively interpret it as a result of evaporative loss of Si from earlier generations of chondrules followed by addition of Si to the precursors of later generation chondrules.

Chondrule

Porphyritic

Pyroxene

Phenocryst

Parent body

10.1111/j.1945-5100.2002.tb00825.x

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Citations (109)

Geochemical and isotopic characteristics of the Cretaceous Orikabe Plutonic Complex, Kitakami Mountains, Japan: magmatic evolution in a zoned pluton and significance of a subduction-related mafic parental magma

Contributions to Mineralogy and Petrology (2003)

Masumi Mikoshiba Satoshi Kanisawa Yukihiro Matsuhisa S. Togashi

Quartz monzonite