Influencia tectónica en el volcanismo Cenozoico del Noroeste argentino


  • F.D. HONGN


A model postulating that the differences in the volcanic evolution between North and South Puna are related to strong variations of the orogenic front development in the foreland is presented. Subandean Belt -Northern part-, Santa Bárbara System -Central part- and Pampean Ranges -Southern part- show different tectonic behaviors due to the mechanic nature of their pre-Andean basement. A thin-skin fault-fold belt developed in the Subandean Belt is a consequence of the presence of a thick Paleozoic sedimentary cover. Thrust progressive migration toward east implicated the displacement of inner orogenic parts on low detachment levels, which sealed magmatic chambers. So, volcanic activity finished or suddenly decreased when the fault-fold belt began to develop in the foreland. On the other hand, mechanic anisotropies of the pre-Andean basement in the Santa Bárbara System and Pampean Ranges controlled and stopped the migration of the orogenic wedge toward the foreland, therefore deformation increased in the inner part of the orogen. Tectonic stacking and the consequent elevation of the back zone of the orogenic wedge would have generated an extensional field for equilibrating the wedge geometry. Normal faults are widespread at South Puna and were the conduits by which big ignimbritic deposits have been extruded at 4 Ma (Laguna Amarga) and 2 Ma (Galán) from medium crust levels and also basalts of less than 1 Ma from upper mantle.