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479 results on '"Ohba, Takeshi"'

1. Rainwater Quality in Some Urban and Rural Sites of Cameroon (Central Africa)

Author

Foupouagnigni, Aicha, Ako, Andrew, Mengnjo, Jude, Eneke, Gloria, Ndjama, Josephine, Nlend, Bertil, Nkeng, George, Ohba, Takeshi, Pisello, Anna Laura, Editorial Board Member, Hawkes, Dean, Editorial Board Member, Bougdah, Hocine, Editorial Board Member, Rosso, Federica, Editorial Board Member, Abdalla, Hassan, Editorial Board Member, Boemi, Sofia-Natalia, Editorial Board Member, Mohareb, Nabil, Editorial Board Member, Mesbah Elkaffas, Saleh, Editorial Board Member, Bozonnet, Emmanuel, Editorial Board Member, Pignatta, Gloria, Editorial Board Member, Mahgoub, Yasser, Editorial Board Member, De Bonis, Luciano, Editorial Board Member, Kostopoulou, Stella, Editorial Board Member, Pradhan, Biswajeet, Editorial Board Member, Abdul Mannan, Md., Editorial Board Member, Alalouch, Chaham, Editorial Board Member, O. Gawad, Iman, Editorial Board Member, Nayyar, Anand, Editorial Board Member, Amer, Mourad, Series Editor, Chenchouni, Haroun, editor, Chaminé, Helder I., editor, Khan, Md Firoz, editor, Merkel, Broder J., editor, Zhang, Zhihua, editor, Li, Peiyue, editor, Kallel, Amjad, editor, and Khélifi, Nabil, editor

Published
2022
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17. Influence of deep magmatic source region in the growth of complex maar‐diatreme volcanoes.

Author

Chako‐Tchamabé, Boris, Graettinger, Alison, Gountié Dedzo, Merlin, Tamen, Jules, Nemeth, Károly, Weber, Bodo, Fozing, Eric Martial, Silis‐Esquivel, Jhoanna, Asaah, Asobo Elvis Nkengmatia, Youmen, Dieudonné, and Ohba, Takeshi

Subjects
VOLCANOES, RESEMBLANCE (Philosophy), ANALYTICAL geochemistry, EXPLOSIVE volcanic eruptions, VOLCANIC ash, tuff, etc., MAGMAS, VOLCANIC eruptions
Abstract

Using a multidisciplinary approach to understand the subsurface processes behind the formation of maar‐diatreme volcanoes is of growing interest. While geophysical characterization can visualize the diatreme and the feeding dike system beneath the volcano at a reasonable scale, such data are rare and generally unavailable. Stratigraphic‐controlled sampling and geochemical analysis of pyroclasts within the ejecta ring can, however, provide substantial information on dike evolution and the influence of the magmatic plumbing system on the growth of these volcanoes. Such investigation is presented here for the Barombi Mbo Maar (BMM), a complex maar of the Cameroon Volcanic Line (CVL) composed of a pile of tephra units linked to multiple explosive phases that were grouped into three eruptive episodes. Major and trace element compositions of lavas collected from the different eruptive units indicate that the erupted magmas at BMM consist mainly of basalt, trachybasalt and basanite, with Oceanic Island Basalts (OIB) and high μ (μ = 238U/204Pb) (HIMU) signatures. Compositional modelling suggests that partial melting occurred at different degrees in the garnet‐to‐spinel transition zone from one episode to another. The repetition of eruptions with big gaps between them, the presence of another large adjacent old maar crater next to the 2.5 km crater of the BMM, and the overall similarity in geochemical compositions from one eruption to another suggest a deep high‐productive zone in the mantle beneath the BMM. The latter productive zone was capable of generating magma batches episodically to fuel several individual monogenetic eruptions at the same location. [ABSTRACT FROM AUTHOR]

Published
2024
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18. Influence of deep magmatic source region in the growth of complex maar‐diatreme volcanoes

Author

Chako‐Tchamabé, Boris, primary, Graettinger, Alison, additional, Gountié Dedzo, Merlin, additional, Tamen, Jules, additional, Nemeth, Károly, additional, Weber, Bodo, additional, Fozing, Eric Martial, additional, Silis‐Esquivel, Jhoanna, additional, Asaah, Asobo Elvis Nkengmatia, additional, Youmen, Dieudonné, additional, and Ohba, Takeshi, additional

Published
2023
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19. Upper Triassic mafic dykes of Lake Nyos, Cameroon (West Africa) I: K-Ar age evidence within the context of Cameroon Line magmatism, and the tectonic significance

Author

Aka, Festus Tongwa, Hasegawa, Takeshi, Nche, Linus Anye, Asaah, Asobo Nkengmatia Elvis, Mimba, Mumbfu Ernestine, Teitchou, Isidore, Ngwa, Caroline, Miyabuchi, Yasuo, Kobayashi, Tetsuo, Kankeu, Boniface, Yokoyama, Tetsuya, Tanyileke, Gregory, Ohba, Takeshi, Hell, Joseph Victor, and Kusakabe, Minoru

Published
2018
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34. Disaster prevention, disaster preparedness and local community resilience within the context of disaster risk management in Cameroon

Author

Aka, Festus Tongwa, Buh, Gaston Wung, Fantong, Wilson Yatoh, Issa, Zouh, Isabella Tem, Djomou, Serges Laurent Bopda, Ghogomu, Richard Tanwi, Gibson, Terry, Marmol del, Mary-Ann, Sigha, Luc Nkamdjou, Ohba, Takeshi, Kusakabe, Minoru, Yoshida, Yutaka, Tanyileke, Gregory, Nnange, Joseph Metuk, and Hell, Joseph Victor

Published
2017
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41. High-precision Δ^′17O measurements of geothermal H2O and MORB on the VSMOW-SLAP scale: evidence for active oxygen exchange between the lithosphere and hydrosphere

Author

Sambuichi, Takashi, Tsunogai, Urumu, Kura, Kazushige, Nakagawa, Fumiko, and Ohba, Takeshi

Subjects
triple oxygen isotopes, geothermal H2O, MORB, rock-water interaction, VSMOW-SLAP scale
Abstract

Recent studies have reported slight but definite differences in Δ^′17O between the lithosphere and hydrosphere. In the present study, we precisely and accurately quantify the Δ^′17O values of geothermal H2O and mid-ocean ridge basalt (MORB) with normalization on the VSMOW-SLAP scale to further substantiate these differences and to discuss the isotopic evolution of the hydrosphere throughout the geologic time scale. With a Δ^′17O value of -60 ± 13 × 10^-6, the Δ^′17O value of MORB is comparable with that in other silicates reported in previous studies. However, the Δ^′17O value of geothermal H2O tended to decrease from +31 × 10^-6 to -51 × 10^-6, which are the usual Δ^′17O values in meteoric water and silicates, respectively, in accordance with the 18O-enrichment. These results imply an active oxygen isotope exchange between silicates and geothermal H2O under high-temperature conditions at depth. This is supported by previous studies which report the 17O-enrichment of silicate altered by hydrothermal H2O. Considering this direct evidence for depletion of 17O, we conclude that the 17O-depleted H2O has been supplied continuously to the hydrosphere. Additionally, low-temperature interaction between the silicates and H2O besides high-temperature hydrothermal interaction must be assumed to explain the observed Δ^′17O of the terrestrial hydrosphere. We conclude that the Δ^′17O of the terrestrial hydrosphere should have been variable throughout the geologic time scale owing to the various oxygen exchange interaction between the lithosphere and hydrosphere.

Published
2021

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