Geochronology and tectonic implications of the Urgamal eclogite, Western Mongolia

• NAEMURA Kosuke

  Nagoya University Museum School of Geology and Mining Engineering, Mongolian University of Science and Technology Department of Geology and Mineralogy, Graduate School of Sciences, Kyoto University

• ERDENEJARGAL Choindonjamts

  Institute of Geology, Mongolian Academy of Sciences

• JAVKHLAN Terbishiinkhen O.

  School of Geology and Mining Engineering, Mongolian University of Science and Technology Institute of Mineral Resources, Chinese Academy of Geological Sciences

• KATO Takenori

  Institute for Space–Earth Environmental Research, Nagoya University

• HIRAJIMA Takao

  Department of Geology and Mineralogy, Graduate School of Sciences, Kyoto University

抄録

The Urgamal eclogite in western Mongolia, described here for the first time, occurs in the Altai allochthon (also known as the Urgamal subzone) in the Zavkhan terrane of the Central Asian Orogenic belt. The eclogite consists of garnet, omphacite, white mica, quartz, epidote, rutile, and barroisite. We measured zircon U–Th–Pb ages in a barroisite–rich sample of the eclogite using an electron probe microanalyzer, which yielded an age of 1113 +31/−52 Ma. This suggests that the eclogite protolith is slightly older than the recorded metamorphic and igneous activity in the Zavkhan autochthon (880–780 Ma). To constrain the timing of eclogite facies metamorphism, K–Ar geochronology was applied to white mica separates, yielding an age of 395 ± 7.9 Ma. This Devonian age is much younger than the time at which the Lake terrane and the Zavkhan terrane collided (545–525 Ma). After the collisional event, the Zavkhan terrane was subjected to extensional tectonics, resulting in alkaline volcanism until the beginning of the Silurian (440 Ma). The Urgamal eclogite records a subduction or collision event at 440–395 Ma, which has not been recognized before. This convergent tectonic environment may have been the result of collision between the Zavkhan terrane and the eastern Tarvagatai terrane. During collision, part of the Altai allochthon may have been subducted beneath the Zavkhan autochthon, thereby forming the Urgamal eclogite.

収録刊行物

• Journal of Mineralogical and Petrological Sciences

  Journal of Mineralogical and Petrological Sciences 115 (4), 357-364, 2020

  一般社団法人　日本鉱物科学会

キーワード

• Eclogite
• Central Asian Orogenic Belt
• Zavkhan terrane
• K–Ar geochronology
• U–Th–total Pb zircon geochronology

詳細情報

• CRID: 1390848250136167040
• NII論文ID: 130007888082
• DOI: 10.2465/jmps.191126
• ISSN: 13493825
• ISSN: 13456296
• Web Site: https://www.jstage.jst.go.jp/article/jmps/115/4/115_191126/_pdf
• 本文言語コード: en
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