The role of cretaceous tectonics in the present-day architecture of the nice arc (Western Subalpine foreland, France)

Abstract

The Nice arc architecture, located at the southern tip of the Western Alps, is very singular, with a strong and narrow curvature. This particular shape could be the result of inherited structures that guide subsequent deformations during compressional events, as has been demonstrated in other parts of the belt. To achieve this objective, we adopted a multidisciplinary approach to characterize the geometry, kinematics, and timing of deformations associated with the various tectonic episodes that structured the arc. A special focus on the Cretaceous formations has revealed that the Cenomanian deposits show significant thickness variations and strong disturbances associated with fault activity. At this time, the formation of narrow, elongated basins was controlled by a system of NNE-SSW trending left-lateral strike-slip faults associated with NW-SE trending normal strike-slip faults and normal faults, dated at 81 ± 13 Ma on calcite recrystallised on the fault planes. During the Cenozoic, two phases of shortening reactivated the faults bounding these basins. An Oligocene phase corresponds to a NE-SW compression, expressed by NW-SE trending folds and thrust and reactivation of first phase faults, dated at 28.7 ± 6.1 Ma, 28.8 ± 8.4 Ma and 27.3 ± 6.3 Ma. The Mio-Pliocene phase is characterised by N-S compression with E-W folds that interfere with the Oligocene folds and reactivate the earlier faults. A Lower Miocene age of 18.2 ± 1.1 Ma and a Pliocene age of 3.16 ± 0.47 Ma pinpoint the timing of these last deformation phases.