Central Andes. Regional The Nazca Plate and Antarctic Plate subduct beneath the South America Plate in the Peru-Chile Trench at a pace of and , respectively, resulting in volcanic activity in the Andes. Present-day volcanism occurs within four discrete belts: The Northern Volcanic Zone (NVZ), the Central Volcanic Zone (CVZ), the Southern Volcanic Zone (SVZ) and the Austral Volcanic Zone (AVZ). These extend between 2°N-5°S, 16°S-28°S, 33°S-46°S and 49°S-55°S, respectively. Between them they contain about 60 active volcanoes and 118 volcanoes which appear to have been active during the Holocene, not including potentially active very large silicic volcanic systems or very small monogenetic ones. These belts of active volcanism occur where the Nazca Plate subducts beneath the South America Plate at a steep angle, while in the volcanically inactive gaps between them the subduction is much shallower; thus there is no asthenosphere between the slab of the subducting plate and the overriding plate in the gaps. Parinacota is part of the CVZ, which contains about 44 active volcanoes. Most volcanoes of the CVZ are relatively poorly researched and many exceed of elevation. Some of these edifices were active during historical time; these include El Misti, Lascar, San Pedro and Ubinas; the largest historical eruption of the CVZ occurred in 1600 at Huaynaputina. Other volcanoes in the CVZ that have been the subject of research are Galan and Purico complex. The CVZ has a characteristically thick crust () and the volcanic rocks have peculiar oxygen and strontium isotope ratios in comparison to the SVZ and NVZ. Parinacota lies in a segment of the CVZ where the Peru-Chile Trench undergoes a 45° curvature, and where the direction of subduction changes from diagonal to perpendicular. The crust is especially thick there, the reasons for this are not agreed upon yet and may vary between the western and eastern sides of the CVZ. Subduction-related volcanism in the region has been ongoing since 200 million years ago, burying most of the Precambrian basement. Various units of sedimentary and volcanic origin form most of the outcropping basement in the region. A dramatic increment of volcanic activity occurred approximately 27 million years ago, when the Farallon Plate broke apart and subduction increased substantially. On the Bolivian side the oldest volcanites are the Oligocene Kollukollu formation 34 million years ago and the 23 million years old Rondal Lavas. Miocene volcanic activity generated the Berenguela, Carangas and Mauri formations,