Structural inheritance and cenozoic stress fields in the Jura fold-and-thrust belt (France)

Abstract

Based on an analysis of 8000 minor fault-slip data in the Jura Mountains (France), we discuss the influence of pre-existing discontinuities on the development of fold-and-thrust belts. We present palinspastic maps showing the stress fields and active faults during the Cenozoic pre-orogenic events in the Jura belt prior to the main Late Miocene fold-and-thrust tectonics. During the Eocene, a N–S strike-slip regime produced a few NNE–SSW sub-vertical strike-slip faults in the central external Jura and a few E–W reverse faults in the eastern Jura near the future frontal thrust. During the Oligocene, an average WNW–ESE extension, with irregular stress trajectories, resulted in normal faulting along N–S to NE–SW trends in the external part of the belt, WNW–ESE trends along the future northern and northeastern frontal thrust, and NW–SE trends in the internal Jura. The Late Miocene tectonics began with a strike-slip regime with a fan-shaped compressional trajectory. It was followed by a stress field with similar stress direction, but local σ 2/ σ 3 stress permutation resulted in strike-slip regime domains contrasting with reverse regime domains. Stress deflections and permutations occurred near inherited cover and basement discontinuities. Major deformation zones, like the Jura frontal thrust onto the foreland, the thrust of the internal central Jura onto the external Jura, and the narrow deformation bands within the flat-lying plateaus formed close to the inherited faults. The structural style of the Jura belt thus partly mimics the pre-orogenic fault pattern. Stress deflections point to the pre-orogenic faults, express the indentation process of the Jura by its hinterland, and highlight successive slip events along major faults during the fold-and-thrust tectonics. This case study illustrates the relevance of minor fault-slip studies for characterizing both the pre-orogenic tectonics and the kinematics of the deformation.