ANDES 125 Figure Map of southern Patagonia and surrounding ocean basins showing distribution of Southern Volcanic Zone (SVZ), Austral Volcanic Zone (AVZ adakites), and Miocene slab melt ‘adakitic’ volcanic centres, deformational styles, plate convergence velocities, and oceanic fracture zones and ridges Active volcanism is absent east of where the Chile Ridge has collided in the last $6 My The boxed region is where features related to ridge collision are best developed (Modified from Gorring ML, Kay SM, Zeitler PK, et al (1997) Neogene Patagonian plateau lavas: continental magmas associated with ridge collision at the Chile Triple Junction Tectonics 16: 17.) Real-like basement The axis of the Recent NVZ arc runs through the valley with volcanic centres occurring from the eastern part of the Western Cordillera into the Subandean Zone The Western Cordillera consists largely of Cretaceous to Eocene oceanic crust, turbidites, and oceanic arc sequences covered by Late Eocene–Oligocene continental sediments and intruded by Eocene and younger magmatic rocks The low-lying, Pacific coastal region is comprised of Cretaceous to Cenozoic basins underlain by oceanic basement Central Andes ($3 to 33 S) The best known part of the Andes is the Central Andes (Figure 4) which can be separated into the Peruvian flat slab segment, the Altiplano–Puna plateau segment that includes the Central Volcanic Zone Arc, and the Chilean flat slab segment A surprising degree of bilateral symmetry exists in the shape of the subducting slab (Figure 2) and the topography of the land surface across the region (Figure 4) Peruvian flat slab segment ($3 S to 15 S) The Peruvian flat slab segment largely coincides with the inactive part of the magmatic arc where active volcanism has been absent from 2.5 to 16 S for the last $3–4 My The Western and Eastern Cordilleras of Ecuador narrow into this region as the Interandean Valley virtually disappears and the Subandean belt broadens to a width of 120–250 km across into the composite Maran˜ on–Ucayali foreland basin A west to east profile shows a topographically low, narrow coastal region west of the Western Cordillera, a narrow Interandean depression, the Eastern Cordillera, the Subandean Zone, and the basins (e.g Madre de Dios) of the eastern lowlands A series of partly submerged Tertiary sediment-filled fore-arc basins (Trujillo, Lima and Pisco) along the narrow