156 ARGENTINA Figure Main orogenic belts in the Andes of Argentina and Chile and adjacent regions From the Tandilian to the Andean, the corresponding geological ages are Early Proterozoic, Middle Proterozoic, Late Proterozoic Early Cambrian, Early Palaeozoic (for both Chanic and Ocloyic), Late Palaeozoic, Late Mesozoic, and Cenozoic domes, with lavas and ignimbritic flows, spread over the Precordillera and the western part of the Sierras Pampeanas as a result of this flattening subduction process Southern Segment South of the Tupungato stratovolcano, at about 33 300 S latitude, active volcanism resumes along the Cordillera Principal and continues down to the southernmost Andes The main Cordillera is composed of a thin to thick-skinned fold-and-thrust belt formed by Jurassic and Cretaceous marine sediments derived from the Pacific Ocean The altitudes, with the only exception being the active volcanic edifices, not exceed 4000–3000 m and are even lower further to the south The Cordillera Frontal, the Precordillera, and the Sierras Pampeanas disappear a few kilometres south of the flat subduction segment The Palaeozoic rocks in the foothills are mildly uplifted in a series of basement blocks, including the San Rafael Block, yet still preserve the Late Palaeozoic peneplain The foreland region has a Late Cenozoic large volcanic plateau that was formed by a few stratovolcanoes of andesitic to dacitic composition, and