 Volcanism in the Chilean Andes is caused by subduction of the Nazca and Antarctic tectonic plates under the South American Plate . Volcanoes in Chile occur in the Central ( CVZ ) , South ( SVZ ) , and Austral Volcanic Zones ( AVZ ) . The gap that separates the Central and South Volcanic Zones is caused by shallow @-@ angle subduction in the Pampean flat @-@ slab segment where the more buoyant Juan Fernández Ridge subducts under the South American continent . This buoyant region prevents the slab ( subducting tectonic plate ) from diving deep into the mantle , where the heat and pressure would destabilize the mineral chlorite , releasing water that would in turn cause melting and volcanism . The Patagonian Volcanic Gap , which separates the South and Austral Volcanic Zones , is caused by the subduction of the Chile Ridge , though it is less clear whether this gap also is due to flat @-@ slab subduction ; it may instead arise because melting of the subducting slab there produced felsic igneous rocks instead of volcanoes . 
