Historia eruptiva de los volcanes monogenéticos de El Toro (23º 05´S ? 66º 42´W), Puna norte, Argentina.

PRESTA, J.F. Y CAFFE, P.J.

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2014 vol. 41 p. 142 - 173

0718-7092

The monogenetic volcanism from the El Toro region (23º 05' S - 66º 42' W) in NW Argentina comprises a group of low-volume (< 5 Km2) mafic volcanic rocks erupted during the Late Miocene-Pliocene in the northern Puna (Andean Central Volcanic Zone). The activity of at least four eruptive centers resulted in the discharge of several lava flows from a cluster of cinder cones, whose architecture coincides with the typical facies model defined for edifices constructed during Strombolian style eruptions. In some cases, volcanoes recorded brief phases of transitional Hawaiian activity that resulted in small and localized fire-fountaining (occasionally with oblique development), responsible for the generation of agglutinated deposits as spatter and clastogenic lava. These highly welded products, still hot and ductile, may have acted as zones of weakness from which the edifices collapsed gravitationally during lava effusions (rafting process). The latter suggests that effusive and pyroclastic eruptions sometimes may have been coeval. Volcanic rocks are geochemically classified as arc-like, high-K calc-alkaline basalts, basaltic andesites and andesites. Although geochemically indistinguishable, some rocks have significantly different petrographic characteristics (phenocryst assemblage, % of crystals). This suggests that some volcanic rocks from El Toro represent the eruption of very similar magma batches that show strong differences in temperature and degree of crystallization, i.e., batches evolving at different crustal depths and/or with different magma chamber residence times. On the other hand, magmas of different chemical compositions were erupted almost simultaneously from the same vents. This intriguing compositional pattern demonstrates that short-lived monogenetic volcanoes may have a complex polymagmatic character.