Neogene sedimentation and tectonics in the Collón Curá basin (Patagonian Andes of Argentina)

We recall here recent developments concerning the filling and paleogeography of the Neogene Collón Curá basin in the foothill of the North Patagonian Andes. To better constrain its evolution, we bring two new 40Ar/39Ar on biotite datings of two ignimbrites that allow bracketing of the filling between 19.04 ± 0.72 and 5.06 ± 0.69 Ma. Like the other intramontane basins of the North Patagonian foothill, the Collón Curá basin initiated around 18 Ma at the time of the Quéchua phase. This corresponds in the area neither to an increase of the convergence rate of the Nazca and South America plates, nor to a significant change in the angle of convergence. We propose to look at this profound alteration of the regional stress regime in the light of the recent results of analog and numerical modeling of subduction. Folding of the slab above the mantle discontinuity at 660 km depth leads to the development of geometries that we retrieve in seismic tomography images in the region. Modeling shows that the overriding plate is coupled to this folding in depth. It suffers from changes in stress (from extensive to compressive stress regime) and topography. It is assumed that a more compressive stress regime will favor the reactivation of border faults of the basin and a regional uplift, hence agradation in basins. On the contrary, subsidence associated with a decrease in shortening will favor the backward erosion that will cannibalize these basins. The life duration of basins will be modulated by efficiency of earth surface processes proper to each watershed (catchment area, river slopes, lithology …). This internal cyclicity of subduction due to slab folding is freed from the kinematics of convergence. It is now necessary to look for the expression of this process in the sequential filling of the basins.