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Carl Alwmark

Carl Alwmark

Senior lecturer

Carl Alwmark

Further evidence for an impact origin of the Tsenkher structure in the Gobi-Altai, Mongolia : Geology of a 3.7 km crater with a well-preserved ejecta blanket

Author

  • Goro Komatsu
  • Jens Ormö
  • Togookhuu Bayaraa
  • Tomoko Arai
  • Keisuke Nagao
  • Yoshihiro Hidaka
  • Naoki Shirai
  • Mitsuru Ebihara
  • Carl Alwmark
  • Lkhagva Gereltsetseg
  • Shoovdor Tserendug
  • Kazuhisa Goto
  • Takafumi Matsui
  • Sodnomsambuu Demberel
Show all

Summary, in English

The Tsenkher structure in the Gobi-Altai, Mongolia is a c. 3.7 km diameter crater with a well-preserved ejecta blanket. It has been hypothesized to be either of impact or volcanic origin in our previous work. Observations during our 2007 expedition and related sample analyses give further support for an impact origin. The evidence includes the presence of a structurally uplifted near-circular rim surrounded by an ejecta blanket, and abundant breccias, some of which are melt- A nd millimetre-scale spherule-bearing. Planar deformation features (PDFs) were found in one quartz grain in a breccia sample. Fe-rich grains are found in a vesicular melt sample that is also characterized by elevated platinum group element (PGE) abundances with respect to the sedimentary bedrock of the area (approximately an order of magnitude). Noble gas analysis of one breccia sample yielded an elevated 3He/4He value of (5.0±0.2) × 10-6. Although not conclusive alone, these geochemical results are consistent with a contribution of meteoritic components. A volcanic origin, in particular a maar formation, would require explanations for the unusual conditions associated with Tsenkher, including its large size occurring in isolation, the structurally uplifted rim and the lack of a bedded base surge deposit. A pronounced rampart structure observed at the eastern ejecta is also unusual for any volcanic origin. 40Ar-39Ar dating of a vesicular melt sample gives an age of the Tsenkher structure of 4.9±0.9 Ma. The rampart structure could provide insights into the formation of similar ejecta morphologies associated with numerous impact craters on Mars.

Department/s

  • Lithosphere and Biosphere Science

Publishing year

2019

Language

English

Pages

1-24

Publication/Series

Geological Magazine

Volume

156

Issue

1

Document type

Journal article review

Publisher

Cambridge University Press

Topic

  • Geology

Keywords

  • breccia
  • ejecta
  • impact crater
  • maar
  • Mongolia
  • raised rim
  • Tsenkher

Status

Published

ISBN/ISSN/Other

  • ISSN: 0016-7568