The Cerro Morado Andesites: Volcanic history and eruptive styles of a mafic volcanic field from northern Puna, Argentina

CABRERA, A.P., CAFFE P.J.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Lugar: Amsterdam; Año: 2009 vol. 28 p. 113 - 131

0895-9811

The Upper Miocene Cerro Morado Andesites constitutes a mafic volcanic field (~100 km2) composed of andesite to basaltic andesite rocks that crop out ~ 75 km to the east from the current arc, in the northern Puna of Argentina. The volcanic field comprises lavas and scoria cones resulting from three different eruptive phases developed without long interruptions between each other. Lavas and pyroclastic rocks are thought to be sourced from the same vents, located where orogen-parallel north-south faults crosscut transverse structures. The first eruptive phase involved the effusion of extensive andesitic flows, and minor Hawaiian-style fountaining which formed subordinate clastogenic lavas. The second phase represents the eruption of slightly less evolved andesite lavas and pyroclastic deposits, only distributed to the north and central sectors of the volcanic field. The third phase represents the discharge of basaltic andesite magmas which occurred as both pyroclastic eruptions and lava effusion from scattered vents distributed throughout the entire volcanic field. The interpreted facies model for scoria cones fits well with products of typical Strombolian-type activity, with minor fountaining episodes to the final stages of eruptions. Petrographic and chemical features suggest that the andesitic units (SiO2 >57%) evolved by crystal fractionation. In contrast, characteristics of basaltic andesite rocks are inconsistent with residence in upper-crustal chambers, suggesting that batches of magmas with different origins or evolutive histories arrived to the surface and erupted coevally.The recognised eruptive styles and lack of volcanic quiescense gaps between eruptions allow classify the Cerro Morado Andesites as a mafic volcanic field, constructed from the concurrent activity of several small, probably short-lived, monogenetic centers.