Geology | Peru Unbound

Geology

Volcanism and the Andes

The Andes are a major geologic feature of Peru. They were formed from a couple of tectonic events. Volcanism first started back in the Triassic period while back-arc basin development didn’t start until the late Jurassic period. Deformation and closure of the back-arc basin began in the Jurassic period and extended from both extremes toward the center. The youngest deformation is observed in the central Chile-Argentina segment, while older sections are found toward the northern and southern ends of the Andes.

Altiplano-Puna Plateau

The most outstanding feature of Peru is the broadening of the main bulk of the Cordillera, embedding the Altiplano and Puna plateaus which have average elevations above 1.8 miles. The Altiplano-Puna plateau is the highest plateau that is associated with abundant magmatism. It is second only to Tibet in height and extent.

Bordering on the west of the Altiplano and Puna plateau is a present day active volcanic arc known as the Western Cordillera. The east side of the paleo-arc is known as the Eastern Cordillera. Each system describes different aspects of the ongoing processes and is characterized by geological and structural differences.

In the Altiplano-Puna plateau we find three different types of volcanic centers. Their spatial and temporal distribution gives important clues of the ongoing tectonic process in the whole area. The main volcanic chain is composed of stratovolcanic complexes and is characterized by thick andesitic and dacitic lavas associated with pyroclastic flows, domes, and hot avalanche deposits. The highest volcanic complexes on the earth can be found in this area, reaching elevations of more than four miles in some cases. The eruptions at high elevations in association with high plumes and strong winds have influenced the distribution of airfall deposits. This means coarse-grained material is localized near the centers while fine-grained particles can be found way into the Chaco foreland.

The plateau (in the back-arc) is characterized by giant andesitic to dacitic ignimbrite sheets, which erupted during the late Miocene-Pleistocene. Some of these are only observable at satellite image scales. These eruptions occurred from huge calderas aligned in parallel to the main arc or on transverse volcanic chains that cross the plateau.

Finally, small mafic monogenetic and fissure flows in the back-arc have been found to be of Oligocene to early Miocene or late Miocene to Recent age. In general, these basaltic to mafic andesitic flows are of mantle origin. They are more abundant in the southern Puna plateau and are associated with extensional or strike-slip faults in the area. Some of them present crustal or shoshonitic chemical signatures.

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