1. Architecture and evolution of Nemegt Uul,
Mongolia: Intraplate mountain building at a
restraining bend in the Gobi Altai Mountains
Stephen Rippington1, Dickson Cunningham1 and
Richard England1
1Crustal Processes Group, Department of Geology,
University of Leicester, UK

2. Gobi Altai
N
Tien Shan

4. Badarch et al. (2002)

5. • Structural and lithological transects
• Geological mapping
• Detailed fault studies
Main objective and methods
Document the structural architecture of the
Nemegt Uul restraining bend and develop an
evolutionary model for the area.

7. Rock types and metamorphic grade
Palaeozoic basement
• Silurian – Carboniferous clastic, and deep
sea sediments, volcaniclastics and volcanics
• Dominantly greenschist facies
• E-W Zone of ophiolitic rocks
• Cumulate gabbro, sheeted dykes,
peridotite, serpentinite and deep sea
meta-sediments

8. Nemegt Uul
Altan Uul
N
20 km

9. Deformation History
Main phases of deformation in Nemegt Uul
• D1: N-S Palaeozoic contraction
• D2: N-S Palaeozoic contraction (progressive
from D1)
• D3: Mesozoic broadly N-S extension and basin
formation
• D4: Cenozoic left-lateral transpression

10. • Folds bedding and forms S1 cleavage
Montage photo
View SE
D1: Upright, open E-W trending F1
fold

11. View E
D2: N vergent
F2 folds

12. View W
D2: N vergent D2 thrust
shear zone cutting F2 folds

13. View E
D3: Normal fault

14. • Left-lateral strike-slip along the Gobi-Tien Shan fault
system
• Restraining bend formation and transpressional flower
structure growth
D4 Transpression

15. View E
N front range bounding thrust
PZ phyllites
Cretaceous clastic basin
sediments

17. View W
S front range bounding thrust

18. Slip Vector

19. View NW

20. View NW

21. Generalised cross section

22. Fault orientations – inherited trends?

23. Summary
• Late Cenozoic transpression along the Gobi-
Altai fault system has formed a long (70km), thin
(15km), bivergent, sigmoidal mountain range.
• Cenozoic deformation is thrust dominated.
• Strike-slip is accommodated along left-lateral
oblique thrusts.
• Cenozoic fault geometry could be inherited from
Palaeozoic basement trends.