Tectonic and magmatic evolution of the Andes Northern Argentina and Chile.

COIRA, B.; J.,DAVIDSON; C.,MPODOZIS Y V.,RAMOS

EARTH-SCIENCE REVIEWS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1982 vol. 18 p. 303 - 332

0012-8252

Two orogenic cycles, both with different evolution, are developed in the western margin of the South American continent in northern Argentina and Chile: the Paleozoic "Hercynic" cycle and the Meso-Cenozoic "Andean" cycle. The Hercynic cycle. A wide marine basin extending westward of the Cordillera Oriental which developed in Cambrian-Ordovician times marks the beginning of this cycle. In contrast to Peru and Bolivia where this basin developed between two Precambrian blocks, the western margin of this basin in northern Argentina and Chile is still unknown. The Ordovician sedimentation and accompanied volcanism ends with the Ocloyic deformation phase and its synkinematic granitic plutonism. Two basins were developed in the Silurian- Devonian separated by the Puna arc, uplifted during this ocloyic phase. The shallow-water marine terrigeneous sediments which were deposited in them were deformed by a new tectono-magmatic associated phase (Chanic phase). Carboniferous to Lower Permian marine carbonates were deposited west of the Puna arc and red beds east of it. Later on, during the Permian to Triassic, a magmatic belt was developed along the Cordillera Occidental. The rhyolites, ignimbrites and the granitic to granodioritic related intrusives are well represented in Chile. Although the overall geologic history of this period is known, many problems concerning its origin and relations to plate tectonics are still unsolved. The Andean cycle. During this cycle, a series of magmatic-arc systems related to the subduction of the Pacific crust was built up along the western margin of South America. Huge volumes of calc-alkaline lavas and related plutons were emplaced since the Jurassic, along belts parallel to the present coastline, showing a general eastward migration trend. Up to the Lower Cretaceous, an ensialic back-arc basin was formed east of this magmatic arc. Thousands of meters of marine and continental sediments were deposited in it. This basin disappeared during the Middle Cretaceous, probably as a result of the final opening of the Atlantic and the active westward movement of the South American Plate. Since Middle Cretaceous times, the magmatic-arc has been the fundamental paleogeographic element. The arc progressively migrated stepwise eastward, each step marked by a tectonic phase. Subduction-related crustal erosion could explain the lack of fore-arc petrotectonic assemblages. The eastward magmatic polarity which characterizes this section of the Andes, could also be explained by such a mechanism.