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Multiple detachments during thin-skinned deformation of the Swiss Central Jura: a kinematic model across the Chasseral

  • Schori, Marc Department of Geosciences, Université de Fribourg, Switzerland
  • Mosar, Jon Department of Geosciences, Université de Fribourg, Switzerland
  • Schreurs, Guido Institut für Geologie, Universität Bern, Switzerland
    09.09.2015
Published in:
  • Swiss Journal of Geosciences. - 2015, vol. 108, no. 2-3, p. 327–343
English Combining field observations, cross-section area balancing techniques and kinematic forward modelling, we present new insights into the evolution of the Jura fold-and-thrust belt in the Chasseral area between Lake Biel and the Vallon de St-Imier, in the Canton of Bern, Switzerland. Our results show that the structures of the Chasseral area and the associated regional uplift can be explained by thin-skinned deformation of the Mesozoic cover, without the need to involve highs in the pre-Triassic basement or invoking detachment folding with thickening of anticlinal cores by flow of Triassic evaporites. According to our thin-skinned model, the overall structure of the Chasseral initiated as a large-scale fault-bend fold, with initial detachment of the Mesozoic cover and NNW-directed movement of material along a basal décollement in Middle Triassic evaporites and important displacement along an upper detachment in the Middle Jurassic Opalinus-Ton Formation. This upper detachment extends from the Seekette to the Vallon de St-Imier (at least 11 km) and further to the north. Deformation above the upper detachment occurs to the north of the Chasseral area and steps back later to form a series of forward-stepping fault-propagation folds at the northern Chasseral mountainside, with associated thrusts that show a typical stair-step geometry due to low-angle breakthroughs. The Seekette anticline on the southern Chasseral mountainside formed due to a late back-stepping backthrust. A total displacement of 11.3 km is inferred that considerably exceeds a displacement estimation of 5.1 km deduced from shortening of the upper boundary of the Jurassic sequence. Forward modelling suggests that material was transported 6.2 km along the Opalinus-Ton detachment resulting in complex deformation to the north of the Vallon de St-Imier because there, folds and thrusts formed above both, the upper detachment and the basal décollement and interacted together.
Faculty
Faculté des sciences et de médecine
Department
Département de Géosciences
Language
  • English
Classification
Geology
License
License undefined
Identifiers
Persistent URL
https://folia.unifr.ch/unifr/documents/304770
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