Colorado Basin 3D structure and evolution, Argentine passive margin

Abstract This 3D structural model of the Colorado Basin provides new insights into the crustal geometry of the basin and its evolution in relation with the Argentine passive margin. Three NW–SE segments (oblique to the N30°E-trending margin) structure the basin. The oldest infill is generally thought to be coeval with the rifting of the South Atlantic margins in Late Jurassic–Early Cretaceous. This coeval development of the Colorado Basin and of the passive margin is still under debate and gives rise to several hypotheses that we investigate in the light of our observations. We propose that reactivation of inherited structures is predominant in the evolution of the Colorado Basin: (1) the Western segment follows the continental continuation of the Colorado transfer zone; (2) the Central segment consists in the continental continuation of the Tona deformation zone; (3) the Eastern segment is superimposed over the Palaeozoic Claromeco Basin. In addition to the 3 segments, the Central High, separating the Central segment to the Eastern segment, corresponds to the Palaeozoic Sierras Australes Fold Belt. The direction of extension responsible for the South Atlantic opening cannot explain the syn-rift infill and thinning of the basin. The structural analysis shows two phases of syn-rift deformation with different directions. Thus, we suggest that the Colorado Basin and the South Atlantic margin are not coeval but that a first extensional event, probably oblique, predates the extension responsible for the South Atlantic opening. This event is then followed by the formation of the N30°-trending distal margin and the reactivation of Palaeozoic N70°-trending faults occurs under the NW–SE opening of the South Atlantic. This two-phase evolution is consistent with the fault chronology and the two directions of thinned crust observed in the distal margin.