The relation of pleistocene monogenetic volcanoes with regional structures in the eastern puna border

PETRINOVIC; GUZMAN; HONGN; DEL PAPA

Jujuy

Congreso; XVII CGA; 2008

AGA

The Puna region, in the southern Central Andes, is characterized by hundreds of Plio-Quaternary mafic, monogenetic volcanoes. These are especially useful to gauge the regional strain field conditions at their respective eruption times, because of their small size, good preservation conditions and absence of overlapping volcanic events. On the other hand, the Andean stratovolcanoes commonly have long periods of activity and specially, they could induce changes in the regional strain field because of their large masses (Tibaldi and Lagmay, 2006; Marques and Cobbold, 2006). These mafic monogenetic volcanoes have been explained by a change in the direction of the minimum principal compression axis, from vertical to horizontal, (Marrett and Emermann, 1992) at Pliocene times. Notwithstanding, there are bulk evidences of coeval thrusting and strike-slip tectonics from the Miocene to the present (Petrinovic et al., 2005; Petrinovic et al., 2006). This relationship is particularly evident in the northern Valle Calchaquí region: divergent thrusts outline both valley borders, develop conjugated en-echelon strike-slip faults and aligned Pleistocene monogenetic volcanoes (Guzmán et al., 2006). Similarly, the Pleistocene monogenetic volcanoes of the Central Puna (i.e. San Jerónimo and Negro de Chorrillos) are set on transference strike-slip faults related to regional thrusts. Thus, varieties of tectonic transference patterns are developed favouring the rise and eruption of magmas from a deep source. These volcanoes are not set directly on the thrust fault planes, but always outline oblique and conjugated fault planes, at both sides of thrust planes. Other volcanic evidences of the regional strain field, such as: a) strike of the lava flows, b) direction of erosion and flank collapses, c) geometry and development of the eruptive vents, craters and cones (Tibaldi, 2005), are not always applicable to these volcanoes, since these directions are often influenced by the slope in relation to the topographic difference at both sides of the thrust plane. Frequent gradients higher than 10º are present in the pre-eruptive basement. That is the reason for the occurrence of some small volume lava flows with considerable length.