underlying rocks as well; Holocene volcanic rocks have little periglacial alteration while older rock formations at times are heavily altered. Lahars also occurred during the history of Parinacota; thick layers of lahar deposits are found on the southern and eastern slopes and form a fan on the northwestern slope of Parinacota. At this fan, lahar deposits reach distances of away from the volcano. Erosion has formed gullies on the upper sector of Parinacota. Otherwise, the volcanic rocks of Parinacota are well preserved owing to the arid climate and the youth of the volcano. Petrology Volcanic rocks erupted by Parinacota range in composition from basaltic andesite to rhyolite. Andesites from the old cone are classified as hornblende and pyroxene andesites. Minerals found within the rocks include amphibole, apatite, biotite, clinopyroxene, iron oxide and titanium oxide, feldspar, olivine, orthopyroxene, pyroxene, sanidine and zircon. Not all of these minerals are found in rocks from all stages of Parinacota. Some of these minerals, such as quartz and sanidine, were at least in part formed by the inclusion of foreign rocks into the magma. Gabbro and granite are found as xenoliths. Overall, volcanic rocks at Parinacota belong to a potassium-rich calc-alkaline suite. The volcanites have characteristically high contents of barium and strontium, especially in the youngest Ajata rocks where their concentration is higher than in any other CVZ volcanic rock. A trend to a more tholeiitic composition in younger eruptions may reflect an increased magma flux and a decreased interaction with the upper crust. The magmas that formed Parinacota and Pomerape are considered to be a group distinct from these that formed older volcanic centres in the region, but also distinct from the magmas that formed the subsidiary vent of Pomerape and the Ajata cones; these tend to be more mafic. In turn, the younger and older Ajata cone lavas have different compositions, one having a high quantity of strontium and the other a low one. Magmas in the Parinacota region formed through distinct processes. One of these is fractional crystallization within closed magma chambers. Another is the mixing of different magmas, one of which in the case of Parinacota may be the Ajata magmas. More specifically, two different magmas with compositions akin to the Ajata magmas contributed the mafic element to the Parinacota magmas. Some differences in magma composition between various volcanoes and stages may reflect the occurrence of several different magma differentiation events.