Andes Tectonic Zonation

The Andean mountain chain is a 5,000-mile- (8,000km-) long belt of deformed igneous, metamorphic, and sedimentary rocks in western south America, running generally parallel to the coast, between the Caribbean coast of Venezuela in the north and Tierra del Fuego in the south. some sections are characterized by active volcanoes, others by their absence. Most of the Andes are located above the subducting Nazca plate except for the southern Andes, which are located above the subducting Antarctic plate. The mountains merge with ranges in Central America and the West Indies in the north, and with ranges in the Falklands and Antarctica in the south. Many snow-covered peaks rise higher than 22,000 feet (6,000 m), making the Andes the second largest mountain belt in the world, after the Himalayan chain. The highest range in the Andes is the Aconcagua on the central and northern Argentine-Chile border. The high cold Atacama Desert is located in the northern Chile sub-Andean range, and the high Altiplano Plateau is situated along the great bend in the Andes in Bolivia and Peru.

The southern part of south America consists of a series of different terranes added to the margin of the Gondwanan supercontinent in the late Pro-terozoic and early Paleozoic. subduction and the accretion of oceanic terranes continued through the Paleozoic, forming an accretionary wedge 155 miles (250 km) wide. The Andes formed as a continental margin volcanic arc system on the older accreted ter-ranes, above a complex system of subducting plates from the Pacific ocean. They are geologically young, having been uplifted mainly in the Cretaceous and Tertiary, with active volcanism, uplift, and earthquakes. The specific styles of volcanism, plutonism, earthquakes, and uplift are found to be segmented strongly into seven main zones in the Andes and related to the nature of the subducting part of the Nazca plate, including its dip and age. Where the subducting slab dips more than 30 degrees beneath south America, the Andes have active volcanism on the surface. In contrast, regions above places where the subduction zone is sub-horizontal do not have active volcanoes, but instead have contraction and sedimentary basin formation.

Although the history of the Andes extends back into the Paleozoic with the accretion of different ter-ranes, especially in the southern parts of the mountain belt, most of the current-day Andean ranges were formed in Mesozoic to recent times. The dominant processes in their formation are related to their location on the leading edge of the convergent plate boundary between south America and the Nazca plate.

Rio Plata Craton

Simple geological map of South America showing the location of the Archean cratons, including the Amazonian craton (AM), Sao Francisco craton (SF), Rio de la Plata craton (RP), Sao Luis cratonic fragment (SL), Luis Alves cratonic fragment (LA). Late Proterozoic orogens and basins surrounding these cratons. The Andean belt forms the western side of South America and includes some Precambrian outcrops (shown in purple). Younger basins including the Amazona, Paraná, and Parnaiba contain thick sequences of Phanerozoic sediments and are drained by large rivers including the Amazon, Río Negro, and Paraná.

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