論文

2021年12月30日

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

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

26
53
開始ページ
1
終了ページ
17
記述言語
掲載種別
研究論文(学術雑誌)
DOI
10.5564/mgs.v26i53.1787
出版者・発行元
Mongolian Journals Online

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 < 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 (<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.

リンク情報
DOI
https://doi.org/10.5564/mgs.v26i53.1787
URL
https://www.mongoliajol.info/index.php/MGS/article/download/1787/1968
ID情報
  • DOI : 10.5564/mgs.v26i53.1787
  • ISSN : 2220-0622
  • eISSN : 2663-5151

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