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The Andes between 36° and 39°S are characterised by the superposition of three different intra-arc basins, which have evolved during the last 25 million years, and the first two of which are separated by tectonic inversion and mountain building processes. This orogenic feature has partially collapsed during the last two cycles of intra-arc extension. The first cycle corresponds to the formation of the Cura Mallin basin, which was developed between 25 and (12?) 10 million years ago (Late Oligocene-Early to Middle Miocene), was inverted between (12-10?) 8 and 5 million years ago (Late Miocene), and resulted in the uplift of a mountain range higher than 2,500 m. The second cycle resulted in the Cola de Zorro basin, which started to develop 5 million years ago (Early Pliocene). This sequence has been deposited since the beginning of its formation over the Cura Mallín orogenic structure, as a consequence of an important extensional collapse or an extensional relaxation of the compressive structure, which depressed this feature below an altitude of 1,200 meters. Along the international border, there are still remnants of the Late Miocene orogen which were preserved as basement highs in the Early Pliocene basin. These structural highs allow the study of the original orogenic structure. The recurrence of intra-arc basins during the last 25 million years was linked both to backward arc migration in that period, as a consequence of the steepening of the Nazca plate, and to structural instability of the orogen related to changes in tectonic boundary conditions.
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