THE TECTONIC STYLE OF THE HIGH CORDILLERA OF MENDOZA (ARGENTINE) : GEOMETRIC, RHEOLOGIC AND CHRONOLOGIC CONTRAINTS ON SECTION BALANCING

Attention is drawn on the tectonic style of that famous fold and thrust belt. The contrasting lithologies involved, the drastic change of facies observed and the superposition of several phases of deformation are emphasized. It is shown that the geometry of folding and thrusting differs notably from the ramp-flat kinematic model. The most significant tectonic features is the labelled Main Andean Overthrust. It marks the eastward backarc thrust of the mesozoic volcanic arc (chilean series) over the andean sedimentary basin (argentinian series). It caused the tectonic collapse of the backarc basin and its conversion into a typical thin-skinned easterly tapering fold and thrust belt. The lack of real transitional facies between both domains provides a paleogeographic argument to consider a good part of the basin is masked tectonically. The basic detachement at oxfordian gypsum level plays a prominent part in the style of the external fold belt. Moreover, it implies the presence of a substantial infragypsum tegument hided below which style is only visible locally. Conversely, the volcanic domain present a mainly monoclinal style but with striking diferential detachments and shearing top to the east owing to some sedimentary intercalations. These imbricate structures respect the stratigraphic order and so may be considered as late morphotectonic structures. The tectonic development started in the Upper Cretaceous and ended in the Late Miocene. It was marked by four main structuring events (Peruvian, Incaic, Pehuenche and Quechuan). The role and style of each phase is stressed. Numerous superimposed structures are described with frequent reactivation by the rear and recognized out-of-sequence propagations. An interpretative profile with subsurface extrapolations is presented to show what kind of structural complexities should be evidenced by sismic profiles and drilling in the future. The role of ductile deformation in deep structures is considered.