Details of the Researcher

PHOTO

Dandar Otgonbayar
Section
Graduate School of Environmental Studies
Job title
Specially Appointed Assistant Professor(Research)
Degree

  • 博士（学術）（東北大学）

  • 修士（環境科学）（東北大学）

Papers 12

  1. Tracking HFSE associated with high salinity fluid during HP metamorphism in the Zavkhan Terrane, Western Mongolia

    Manzshir Bayarbold, Atsushi Okamoto, Masaoki Uno, Otgonbayar Dandar, Mayuko Fukuyama, Geri Agroli, Noriyoshi Tsuchiya

    Lithos　490-491　2024/12/15

    DOI： 10.1016/j.lithos.2024.107853 　

    ISSN： 0024-4937

    eISSN： 1872-6143

  2. Characterization of serpentinization in olivine-orthopyroxene-H<inf>2</inf>O system revealed by thermogravimetric and multivariate statistical analyses

    Atsushi Okamoto, Shuhei Tanaka, Masaoki Uno, Otgonbayar Dandar, Kazuki Yoshida

    Island Arc　33　(1)　2024

    DOI： 10.1111/iar.12519 　

    ISSN： 1038-4871

    eISSN： 1440-1738

  3. Multiphase-solid fluid inclusions in HP-LT eclogite facies rock (Zavkhan Terrane, Western Mongolia): evidence for the evolution from saline to hypersaline fluids during metamorphism in subduction zone

    Manzshir Bayarbold, Atsushi Okamoto, Masaoki Uno, Kenta Yoshida, Alexey Kotov, Geri Agroli, Otgonbayar Dandar, Yasuhiro Niwa, Masao Kimura, Noriyoshi Tsuchiya

    Contributions to Mineralogy and Petrology　178　(11)　2023/11/04

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1007/s00410-023-02055-3 　

    ISSN： 0010-7999

    eISSN： 1432-0967

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    Abstract Fluid inclusions in high- and ultrahigh-pressure metamorphic rocks provide direct information on the composition of the fluids that evolved during metamorphism and fluid-rock interactions in deep subduction zones. We investigate the fluid inclusions in the Khungui eclogite of the Zavkhan Terrane, Central Asian Orogenic Belt. Fluid inclusions are observed in garnet and quartz in the eclogite samples that underwent metamorphism during subduction. The primary fluid inclusions in quartz are composed of liquid and vapor with high salinities (15.7–16.4 wt.% NaCl eq.), whereas the secondary fluid inclusions in quartz are classified as: relatively high salinity (Type I:12.5–16.3 wt.% NaCl eq.) and low salinity (Type II:6.7–10.6 wt.% NaCl eq.). The garnet shows compositional zoning from Ca-poor cores to Ca-rich rims, and the rims that grew during the eclogite-stage metamorphism (2.1–2.2 GPa at 580–610 °C) preferentially contain numerous primary fluid inclusions. The primary fluid inclusions in garnet are commonly bi-phases (liquid and vapor); however, some are multiphase-solid fluid inclusions composed of fluids (liquid and vapor) and combinations of several minerals (halite, quartz, apatite, calcite, biotite, chlorite, and actinolite). Bi-phase fluid inclusions preferentially occur in the inner parts of the Ca-rich garnet rim, whereas multiphase-solid fluid inclusions occur along the margins of the Ca-rich rim. We hypothesize that the multiphase-solid fluid inclusions are formed via interactions between trapped fluids, trapped minerals, and the host garnet during exhumation. By combination of FIB–SEM and synchrotron X-ray CT analyses, the detailed occurrences, volumes, and compositions of the solid phases in the fluid inclusion was analyzed. We then conduct mass balance analysis to reconstruct accurate fluid compositions using data from the FIB–SEM and synchrotron X-ray CT images of the multiphase-solid fluid inclusion. The results of these analyses reveal that (1) fluid changed from an H2O-dominated saline fluid (13–16 wt. % NaCl eq.) at the prograde to the earlier eclogite stage to H2O–CO2-dominated hypersaline fluid at later eclogite stage (~ 32 wt. % NaCl eq., 7.3 wt. % CO2 and ~ 19 molal dissolved cations); (2) a variety of mineral assemblages in multiphase-solid fluid inclusions are produced by post-entrapment reactions between the trapped hypersaline fluid, trapped minerals and the fluid host mineral. The evolution of fluids from saline to hypersaline during the eclogite facies stage is probably caused by the formation of hydrous minerals (i.e., barroisite) under a near-closed system.

  4. Mantle hydration initiated by Ca metasomatism in a subduction zone: An example from the Chandman meta-peridotite, western Mongolia

    Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Noriyoshi Tsuchiya

    Lithos　452-453　107212-107212　2023/09

    Publisher: Elsevier BV

    DOI： 10.1016/j.lithos.2023.107212 　

    ISSN： 0024-4937

  5. Progressive carbonation and Ca-metasomatism of serpentinized ultramafic rocks: insights from natural occurrences and hydrothermal experiments International-journal Peer-reviewed

    Nomuulin Amarbayar, Otgonbayar Dandar, Jiajie Wang, Atsushi Okamoto, Masaoki Uno, Undarmaa Batsaikhan, Hideko Takayanagi, Yasufumi Iryu, Noriyoshi Tsuchiya

    Contributions to Mineralogy and Petrology　178　2023/06

    Publisher: SpringerNature

    DOI： 10.1007/s00410-023-02013-z 　

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    Hydration, carbonation, and related metasomatism of mantle peridotite play a significant role in the global geochemical cycle. In this study, we combined an analysis of carbonated serpentinite with hydrothermal experiments on carbonation and Ca-metasomatism for samples from the Manlay ophiolite, southern Mongolia to investigate that carbonation mechanism of the serpentinite body after serpentinization. Samples show that the serpentinite was either transected by calcite and dolomite veins or was completely replaced by carbonates (calcite with minor dolomite) and quartz, in which the original mesh texture of serpentinite was preserved. Carbonation occurred after low-temperature serpentinization (lizardite/chrysotile), suggesting that carbonation occurred at temperatures lower than 300 ˚C. Calcite in the serpentinite showed δ13 CVPDB values ranging from -8.83 to -5.11 ‰ and δ18 OVSMOW from + 20.1 to + 24.4 ‰, suggesting that CO2 in the fluids could be derived from the degradation of organic material or methanotrophic processes rather than the origin of seafloor limestone. Three batch-type experiments, i.e., single step experiments (1) Olivine + NaHCO3,aq + CaCl2,aq and (2) Chrysotile + NaHCO3,aq + wollastonite (Ca source), and two steps experiment (3) Olivine carbonation and Ca-metasomatism, were conducted at 275 °C and 5.7 MPa to constrain the mechanism of calcite replacement of serpentinite. We found that calcite precipitated from the solution directly in the first two experiments, but replacement of serpentinite by calcite was not observed. In contrast, the third experiment caused the initial carbonation to form magnesite and then changed to calcite by later alteration. The natural occurrences and experiments revealed the possibility that the carbonation of olivine followed by Ca-rich fluid infiltration produced calcite in the carbonated serpentinite. Such Ca-metasomatism of Mg carbonates could easily occur in the ultramafic bodies and significantly affect the global carbon cycle.

  6. NaHCO3 as a carrier of CO2 and its enhancement effect on mineralization during hydrothermal alteration of basalt

    Sena Kikuchi, Jiajie Wang, Otgonbayar Dandar, Masaoki Uno, Noriaki Watanabe, Nobuo Hirano, Noriyoshi Tsuchiya

    Frontiers in Environmental Science　11　2023/02/15

    Publisher: Frontiers Media SA

    DOI： 10.3389/fenvs.2023.1138007 　

    eISSN： 2296-665X

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    Reaction of carbon dioxide (CO2) with minerals to generate stable carbonates, also known as CO2 mineralization, has been regarded as one of the most promising methods for safe and permanent carbon storage. As a promising feedstock, basaltic rock has gained special interest, and elevating basalt carbonation efficiency with the reduction of negative environmental impact is the main challenge for CO2 mineralization system development. Considering multiple potential positive effects of the CO2 carrier, NaHCO3, we conducted this study to experimentally evaluate the CO2 storage efficiency during water-basalt-NaHCO3 interactions under hydrothermal conditions at 200–300°C. The inclusion of NaHCO3 was confirmed to drastically promote the alteration of basalt, especially at higher temperatures. As revealed by experiments conducted at the saturated vapor pressure of water, the carbon storage efficiency at 300°C reached 75 g/kg of basalt in 5 days, which was 12 times higher than that at 200°C. In such hydrothermal systems, basalt was carbonated to generate calcite (CaCO3), where the Ca was mainly from plagioclase; Mg and Fe were incorporated into smectite, and Na in the saline system participated in the formation of Na silicates (i.e., analcime in the case of basalt). Due to the presence of additional Na in solution, all the released elements were consumed quickly with generation of secondary minerals in turn promoted basalt dissolution to release more Ca for CO2 storage. This study illuminated the role of NaHCO3 in basalt carbonation and provided technical backup to the design of advanced CO2 mineralization systems.

  7. Continental arc-derived eclogite in the Zavkhan Terrane, western Mongolia: Implications for the suture zone in the northern part of the Central Asian Orogenic Belt

    Manzshir Bayarbold, Atsushi Okamoto, Otgonbayar Dandar, Masaoki Uno, Noriyoshi Tsuchiya

    Journal of Asian Earth Sciences　229　2022/05/15

    DOI： 10.1016/j.jseaes.2022.105150 　

    ISSN： 1367-9120

  8. Formation of the garnet aggregate of the Khungui eclogite in the Zavkhan Terrane, Western Mongolia

    Manzshir Bayarbold, Atsushi Okamoto, Otgonbayar Dandar, Masaoki Uno, Noriyoshi Tsuchiya

    2022/03/28

    Publisher: Copernicus {GmbH}

    DOI： 10.5194/egusphere-egu22-6935 　

  9. Multi-stage serpentinization of ultramafic rocks in the Manlay Ophiolite, southern Mongolia

    Amarbayar Nomuulin, Noriyoshi Tsuchiya, Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Undarmaa Batsaikhan, Jiajie Wang

    Mongolian Geoscientist　26　(53)　1-17　2021/12/30

    Publisher: Mongolian Journals Online

    DOI： 10.5564/mgs.v26i53.1787 　

    ISSN： 2220-0622

    eISSN： 2663-5151

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    Serpentinization of ultramafic rocks in ophiolites is key to understanding the global cycle of elements and changes in the physical properties of lithospheric mantle. Mongolia, a central part of the Central Asian Orogenic Belt (CAOB), contains numerous ophiolite complexes, but the metamorphism of ultramafic rocks in these ophiolites has been little studied. Here we present the results of our study of the serpentinization of an ultramafic body in the Manlay Ophiolite, southern Mongolia. The ultramafic rocks were completely serpentinized, and no relics of olivine or orthopyroxene were found. The composition of Cr-spinels [Mg# = Mg/(Mg + Fe2+) = 0.54 and Cr# = Cr/(Cr + Al) = 0.56] and the bulk rock chemistry (Mg/Si = 1.21–1.24 and Al/Si &lt; 0.018) of the serpentinites indicate their origin from a fore-arc setting. Lizardite occurs in the cores and rims of mesh texture (Mg# = 0.97) and chrysotile is found in various occurrences, including in bastite (Mg# = 0.95), mesh cores (Mg# = 0.92), mesh rims (Mg# = 0.96), and later-stage large veins (Mg# = 0.94). The presence of lizardite and chrysotile and the absence of antigorite suggests low-temperature serpentinization (&lt;300 °C). The lack of brucite in the serpentinites implies infiltration of the ultramafic rocks of the Manlay Ophiolite by Si-rich fluids. Based on microtextures and mineral chemistry, the serpentinization of the ultramafic rocks in the Manlay Ophiolite took place in three stages: (1) replacement of olivine by lizardite, (2) chrysotile formation (bastite) after orthopyroxene and as a replacement of relics of olivine, and (3) the development of veins of chrysotile that cut across all previous textures. The complex texture of the serpentinites in the Manlay Ophiolite indicates multiple stages of fluid infiltration into the ultramafic parts of these ophiolites in southern Mongolia and the CAOB.

  10. Redistribution of magnetite during multi-stage serpentinization: Evidence from the Taishir Massif, Khantaishir ophiolite, western Mongolia

    Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Noriyoshi Tsuchiya

    Journal of Mineralogical and Petrological Sciences　116　(3)　176-181　2021

    DOI： 10.2465/jmps.201130a 　

    ISSN： 1345-6296

    eISSN： 1349-3825

  11. Formation of secondary olivine after orthopyroxene during hydration of mantle wedge: evidence from the Khantaishir Ophiolite, western Mongolia

    Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Ryosuke Oyanagi, Takayoshi Nagaya, Ulziiburen Burenjargal, Tsuyoshi Miyamoto, Noriyoshi Tsuchiya

    Contributions to Mineralogy and Petrology　174　(11)　2019/11/01

    DOI： 10.1007/s00410-019-1623-1 　

    ISSN： 0010-7999

    eISSN： 1432-0967

  12. DRONE BRINGS NEW ADVANCE OF GEOLOGICAL MAPPING IN MONGOLIA: OPPORTUNITIES AND CHALLENGES Peer-reviewed

    Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Undarmaa Batsaikhan, Burenjargal Ulziiburen, Noriyoshi Tsuchiya

    Mongolian Geoscientist　47　53-57　2018

    DOI： 10.5564/mgs.v0i47.1063 　

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