The different volcanic zones are intercalated by volcanic gaps, zones that, despite lying at the right distance from an oceanic trench, lack volcanic activity. The Andes has three major volcanic gaps the Peruvian flat-slab segment (3 °S—15 °S), the Pampean flat-slab segment (27 °S—33 °S) and the Patagonian Volcanic Gap (46 °S—49 °S). The first one separates the Northern from the Central Volcanic Zone, the second the Central from the Southern and the last separates the Southern from the Austral Volcanic Zone. The Peruvian and Pampean gaps coincide with "flat slab" (low angle) subduction areas and therefore the lack of volcanism is believed to be caused by the shallow dip of the subducting Nazca Plate in these places. The shallow dip has in turn been explained by the subduction of the Nazca Ridge and the Juan Fernández Ridge for the Peruvian and Pampean gaps respectively. Since the Nazca and Juan Fernández Ridge are created by volcanic activity in Pacific hotspots (Easter and Juan Fernández) it can be said that volcanic activity in the Pacific is responsible for the suppression of volcanism in parts of the Andes.
The Patagonian gap is different in nature as it is caused not by the subduction of an aseismic ridge but by the subduction of the Chile Rise, the boundary ridge between the Nazca and the Antarctic Plate.
Read more about this topic: South Volcanic Zone
... The Pampean gap or Norte Chico separates the Andes Central and Southern volcanic zones ...
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