Soledad caldera

The Altiplano is a basin of Cretaceous-Cenozoic age in Peru and Bolivia and embedded between the Western Cordillera, a Mesozoic-Cenozoic volcanic arc and the Eastern Cordillera which is a Paleozoic fold belt. The development of the Altiplano started during the Neocomian[1] and continued during the Tertiary, with several tectonic episodes resulting in the folding of the rocks.[2]

During the Miocene, intrusive volcanism occurred along the eastern margin of the Altiplano (the Coniri fault) and resulted in the formation of epithermal mineral deposits,[2] which extend from Tiwanaku in the northwest to Oruro in the southeast.[3]

The Soledad caldera lies northwest of Oruro,[4] between the Desaguadero River and Caracollo.[5]

The caldera is somewhat elongated with dimensions of 14 by 22 kilometres (8.7 mi × 13.7 mi).[6] It contains an ephemeral lake, Lago Soledad,[4] which only fills during wet years and the only in the eastern half of the caldera.[7]

The Soledad tuffs are exposed in particular on the eastern margin of the caldera,[5] where they form dacitic deposits with thicknesses of over 130 metres (430 ft) thickness.[8] These tuffs cover surfaces of about 90–100 square kilometres (35–39 sq mi).[7] They are not very conspicuous in satellite images, whereas on the southern side a group of lava flows forms the more noticeable Esquentaque complex.[9]

The Soledad caldera has erupted dacitic material rich in potassium, fitting into the calc-alkaline system.[10] Minerals found within the material include apatite, biotite, hornblende, plagioclase, pyroxene, quartz and sanidine.[11]