Thomas Voigt 1 Jonas Kley 2 Christoph Wehner 1 1 FriedrichSchillerUniversität Jena Institut für Geowissenschaften Germany voigtgeounijenade 2 ID: 1014238
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1. A mountain of folds: triangle zone in the fold-and-thrust belt of the External Pamir, KyrgyzstanThomas Voigt1, Jonas Kley2, Christoph Wehner1 1Friedrich-Schiller-Universität Jena, Institut für Geowissenschaften, Germany (voigt@geo.uni-jena.de) 2Georg-August-Universität Göttingen
2. A triangle zone is exposed in the External Pamir FTBPik Sverdlova triangle zone
3. Regional cross section, Altyn Dara ValleyAlai Valley
4. Satellite image of the Pik Sverdlova triangle zone (Google Earth)
5. LowerCretaceousUpperCretaceousMarker 2Marker 1The Upper Cretaceous succession forming the face of Pik Sverdlova has only some 400 m of original thickness
6. Lower CretaceousNSUpper CretaceousBackthrustThe limestone markers exhibit relatively constant thickness and seem to have experienced limited penetrative deformation and length change.Notice rotated thrust fault, also suggesting little stretching of fold limbs.
7. The sinuous length of Marker 1 in this view is 10,5 km, shortened to 1,6 km (85% shortening).The shale intervals show strong slaty cleavage and marked thickness changes. Dividing the area of the dark shales by sinuous length gives only 65 m of average thickness. Marker 1
8. Original thickness and volume lossSNLower CretaceousCenomanian-TuronianLower Detachment8The dark shales are approximately 150 m thick in a less deformed section further east, near Pik Lenin. If this value is similar to the original thickness at Pik Sverdlova, volume loss in the shales could be as high as 50-60%.Notice folded limestone layer between two detachments in this section.Upper DetachmentFolded limestone
9. Evolution of the triangle zone (and of hypotheses)Thrust fault propagates along detachment near base Upper Cretaceous until obstacle, tentatively shown as growth normal fault.9 km of Upper Cretaceous strata pile up. Thrust fault through Lower Cretaceous bypasses obstacle……and creates backthrust. Alternatively, the backthrust could originate early on and itself form the obstacle.Lower Cretaceous
10. ConclusionsThe Pik Sverdlova triangle zone looks awesomeIt may be one of the best exposed triangle zones worldwideDifferent from most models the triangular region between the main fore- and backthrusts is dominated by tight folds Piling up of > 9 km of bed length in upright isoclinal folds suggests a very efficient detachment with an abrupt termination on the foreland sideWe speculate that folding may be an important process in other triangle zones, too.