Peru-Chile Trench after metamorphosis. This magma melted part of the mantle wedge above the subducting plate, mixing with the melt products. Further contamination by crustal Tonalite-Trondhjemite-Granodiorite-like rocks from the Archean, crystal fractionation and magma mixing further up in the crust then yielded the Licancabur magmas. The younger lavas may have formed from the mixing of dacite with the magmas forming the older lavas. Some inclusions in Licancabur rocks seem to have originated as wall rocks of the magma chamber. Xenoliths containing gabbro are also found. Unlike neighbouring volcanoes, such as Saciel at Sairecabur (further north) and Tocol (further south), there appear to be no sulfur deposits on Licancabur. Climate and ecosystem The region's climate has been dry since the Tertiary. The area around Licancabur is dominated by year-round high pressure caused by the South Pacific High, giving it a very sunny climate. Because of the lack of moisture, the energy from solar radiation is dissipated primarily by wind. In the Llano de Chajnantor area, wind generally reaches its maximum strength during the day. Its prevailing direction is from the west, except in summer when winds are more variable. Because of the area's tropical location (where the ozone layer is thinner) and high altitude, it receives a large amount of ultraviolet (UV) radiation. The world's highest level of UV radiation (UV index of 43.3>) was reported from Licancabur, although the high irradiation might have caused measurement artifacts. Air temperatures obtained at the lake in Licancabur's crater range from . According to observers in 1955, temperatures at the Licancabur summit were always below freezing, sometimes falling below . At Llano de Chajnantor, southeast of Licancabur, weather records indicate that maximum temperatures range from . Average precipitation on Licancabur is estimated at per year, but snowfall probably exceeded in 1955. Snow has been recorded at Llano de Chajnantor when in summer easterly winds transport moisture from the Amazon to the area. Licancabur has no persistent snowpack; snow deposited by storms usually disappears within a few days. In sheltered areas, however, it can persist for months, and a 1985 map shows a persistent snow/ice cover at the summit. The elevation of the snow line at Licancabur is estimated to be . Licancabur is part of the Eduardo Avaroa Andean Fauna National Reserve. Vegetation at lower altitudes is typical of a high tropical desert climate. Three biozones have been described in the region: an Andean