CENOZOIC EVOLUTION OF THE CORDILLERA ORIENTAL BETWEEN 22° TO 23° S

The sedimentary basins of Pozuelos, Tres Cruces, Santa Victoria Range and Western Subandean Ranges basins are considered. During the Eocene to the Lower Oligocene (50 – 28 Ma) an orogenic front could have uplifted in the west of the region and could have generated a foreland basin over the old Cretaceous depocentre of Tres Cruces. During the Upper Oligocene to the Lower Miocene (28 – 16 Ma) a piggyback basin is developed in Pozuelos area, which is evidenced by the Moreta Formation and a reduced volcanic activity is registered. During the Middle to the Upper Miocene (16 – 9 Ma) a new compressive process would have begun. The Tres Cruces basin which developed formerly as a foreland basin, is incorporated to the orogenic system and continued its evolution as a piggyback basin. In the Puna, an increasing of volcanic activity is registered. During the Upper Miocene (9 – 6 Ma) should be a period of aparent tectonic calm in the orogenic front, which was located in the Santa Victoria Range. During this time, tectonic activity was developed as out-of-sequence thrusts behind the orogenic front. This event produced a crustal thickening of the Puna and part of the Eastern Cordillera. The huge calderas and ignimbritic centres of the Puna, in the Upper Miocene, are the product of an important crustal fusion. A new piggyback basin was developed over the Santa Victoria range. During Upper Miocene to the Pleistocene (< 6 Ma) the orogenic front migrated to the east. A new decollment level affecting the Precambrian basement developed a thick skinned structure in the Eastern Cordillera. The Subandean Ranges show a thin skinned fold and thrust belt. The exhumation of this thrust is linked with deposition of conglomerates of the Terciario Subandino Superior. The Subandean Front has been active during the Quaternary as evidenced by the deformed Pleistocene conglomerate of the Simbolar Formation. The volcanic arc in the Puna region migrated to the west towards the Cordillera del Límite.