A distinction must be made between folds and uplifts of the Andes Mountains. All the Andean folding was done during the Middle Cretaceous. Still, only part of its uplift continued during the third with a peneplain, which was later raised 3,000 meters from the Central Andes Aconcagua mountain guides.
The collapse of the Central Valley occurred during the Upper Pliocene, before the great ice ages, and appears to be continuing. In reality, both the Andes’ rising and the Central Valley’s sinking have been done slowly (even on a geological scale) and possibly in numerous phases. Like most Central Andes, this knot comprises acid lavas: porphyrites with visible grains but without phenocrysts. They are attributed to the Cretaceous since further east (in Polleras and Alto Yeso), the limestone layers very rich in fossils of the Lower Cretaceous are intertwined.
The potency of these layers of porphyrite is more than 3000 meters. Their stratification is horizontal, except in the southeast part, where they fall towards the east to become vertical in Cerro Tronco. During the Jurassic, Aconcagua ascents layers of very thick volcanic lavas appeared: Porphyrites in the Central Andes, porphyries, quartziferous in Patagonia. From the Cretaceous, continental sediments (schists) are today in the Patagonian Pampas, alternating with marine ones (limestones and sandstones). In the Central Andes, porphyrite effusions continue during the lower Cretaceous with some deposits of fossiliferous limestone (sometimes later transformed into gypsum) and sandstones. During the Middle Cretaceous (Senonense), the marine conglomerates of Quiriquina were deposited at some coast points. The lower third (Eocene) is continental, but in the middle third (Oligocene), there was a massive marine invasion. During the end of the Miocene and the Lower Pliocene, the remarkable effusions of andesites, trachytes, and basalts occur, both in the central border range and in all the Patagonian plateaus to the east of the mountain range. The Aconcagua treks The knot of Nevado Juncal (Argentine-Chilean border) essentially corresponds to a high rectangular table measuring 21 x 8 kilometers, elongated in a northeast-southwest direction, with a height ranging between 3,600 and 4,600 meters, with two bastions at its extremities: the Nevado Juncal to the northwest and the Cerro de Plomo group to the southwest. Five large snowdrifts almost entirely cover this high plateau. The Escondido Glacier, the three Olivares Glaciers and the Juncal Sur Glacier. The first flows north and the other four south. The climate of the Andes, in general, is determined by several factors; the Humboldt and Patagonian marine currents, the winds, and orography. The Humboldt (cold) and Patagonian (temperate) currents bathe Chile’s north and south coasts, respectively. It turns out that the winds and their orography determine the climate of the Central Andes, and since the predominant wind is the dry southwest, during the summer, there is no precipitation and not even clouds.