Laguna Amarga

Laguna Amarga is a caldera and associated ignimbrite in the Andes of northwestern Argentina.
Laguna Amarga is part of the southern Central Volcanic Zone and one among several Miocene-Pliocene-Pleistocene volcanic centres of this volcanic region. The formation of magma chambers and thus of large volcanic systems has apparently been influenced by tectonic changes. The Laguna Amarga caldera is associated with the Cordillera Claudio Gay faults together with the Laguna Escondida and Wheelwright calderas, all of which are between 6.5 and 4 mya old. Laguna Amarga and Laguna Verde are sometimes associated with the Vallecito ignimbrite instead. The formation of the Laguna Amarga volcanic centre was probably influenced by orogenic changes in the Andes which triggered the formation of fractures in the crust.
The Laguna Amarga caldera has a diameter of and is linked to the Laguna Escondida caldera. It is the largest caldera in the area.
The Laguna Verde ignimbrite was erupted 4-3 mya ago and is associated with these two calderas. Other dates are 4.5 ± 0.5 to 3.0 ± 0.2 mya. The ignimbrite covers an area of , cropping out southwest of the Laguna Amarga ignimbrite. The Laguna Verde ignimbrite ranges from dacite to rhyolite in composition, containing biotite, pumice, quartz and sanidine.
The Laguna Amarga ignimbrite was erupted 5.1 mya ago, or 3.7-4.1 mya, and it has a volume of over . It extends north-northwest from Peinado volcano. The ignimbrite is somewhat welded and contains vesicular pumice, and bears some similarity with the Cyclops ignimbrite away. Further, the Laguna Amarga ignimbrites like the Cerro Blanco and Galan ignimbrites are rich in sodium. It covers a surface area of , cropping out around the Laguna Amarga. Another ignimbrite, Los Colorados, is located at the edge of the Amarga caldera but its eruptive centre is unknown. After its formation, lava flows from Cerro El Condor overran the floor of the caldera and monogenetic volcanos developed both on the caldera floor and on its ignimbrite.