Аргентинадағы Антофагаста-де-ла-Сьерра жанартау алабы

Volcanic field in Argentina

The Antofagasta de la Sierra volcanic field lies within the north–south trending tectonic depression of the same name, Of the individual vents the La Laguna and Alumbrera cones are the best studied ones, they lie about south of Antofagasta de la Sierra. These volcanoes are associated with black lava flow fields. and are located south of the Antofagasta de la Sierra lake. To their northwest lies Cachamani. Alumbrera cone is high and has an elliptical shape with a maximum length of , probably due to wind influencing the growth of the cone. The cone shows signs of having been gravitationally unstable, including a sector collapse on its northwestern flank. The cone has a wide crater and a few fissure vents. Alumbrera has a volume of and is the source of a large lava flow field which covers a surface of

La Laguna is smaller than Alumbrera: The cone is only high and wide, with a deep crater. As with Alumbrera La Laguna features one fissure vent and a lava flow field, with a smaller volume of and surface area of
Both La Laguna and Alumbrera were fed by northwest striking fissures, which is unusual as most lineaments in the area strike northeastwards or north–south. The surfaces of erupted rocks have been subject to various degrees of wind driven erosion which has left grooves in the most altered units.

Alumbrera and La Laguna has erupted alkaline to sub alkaline basaltic trachyandesite to trachybasalt with a porphyritic texture. Phenocrysts within the rock include olivine and plagioclase or clinopyroxene, which form also the bulk of the matrix. including "alum" (in reality a mixture of aluminium sulfate and magnesium sulfate) found at Alumbrera, were mined by the local population.

Eruptions at Alumbrera occurred in two phases, the first formed toothpaste lava and aa lava and the second in addition to lava small pyroclastic flows and a tephra blanket. A scoria fallout is found as far as east of Alumbrera. During this second phase, the sector collapse at Alumbrera occurred and was followed by the emission of lava bombs during Strombolian eruptions. Later during a second phase of activity lava bombs and scoria formed a newer cone and two lava flow fields. At both volcanoes, phreatomagmatic activity may have occurred after the magma pressure dropped so far that water could enter the conduit. The eruptions probably lasted several weeks to several years. A lava flow at La Laguna cone has been dated to 340,000 ± 60,000 years before present, A large scale research project in the Puna yielded a number of Ar Ar and K Ar dates, including 3.2 and 4.5 million years ago for Jote and 0.3 and 7.3 million years ago for Alumbrera and La Laguna. The older age appears to refer to a mesa just west of the Alumbrera lava field. The youngest age was obtained on Alumbrera cone by argon argon dating: 37,000 ± 2,000. Historical activity is unknown, In 1907 the volcanoes were considered to be extinct, but the field may have had eruptions during the Holocene; The Antofagasta River coming from the north forms a large wetland before the relatively deep Antofagasta lake; the Alumbrera volcano borders the lake in the south. The lake in 1911 consisted of two halves, joined by a canal. Before the emplacement of the volcanic field, which dammed the lake, the river may have continued south to Carachipampa. A major archeological site is emplaced on the Antofagasta volcano.