Volcanological and geochemical evolution of the Diamante Caldera-Maipo volcano complex in the southern Andes of Argentina (34° 10´S)

PATRICIA SRUOGA; EDUARDO JORGE LLAMBÍAS; LUIS FAUQUÉ; DAVID SCHONWANDT; DAVID REPOL

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Lugar: Amsterdam; Año: 2005 vol. 19 p. 399 - 414

0895-9811

Abstract             Two main stages are distinguished in the evolution of the Diamante Caldera-Maipo Volcano Complex. “Diamante stage” corresponds to the emplacement of large-volume rhyolitic ignimbrites associated to a 20 by 16 km in diameter collapse caldera. This ~0.45 Ma catastrophic event was followed by the “Maipo stage” which represents the last 100 ka of the complex lifetime. Field work and Ar/Ar data support an eruptive record within the Maipo stage consisting of at least 4 pre-last glacial maximum (pre-LGM) large-volume events and 3 post-glacial small-volume events. Historic activity remains uncertain. At present, neither fumarolic activity nor hydrothermal manifestations are detected. Dominantly effusive, Maipo stage includes blocky and flow-banded lavas, a ring-fault dome and subordinated pyroclastic deposits. They define a high-K, calc-alkaline suite ranging in silica from 53%  to 68% and encompassing two pyroxene with minor olivine andesites and two pyroxene and hornblende bearing dacites. Within the volcanic complex a general geochemical trend towards more evolved and potentially higher explosive products is recognized. Differentiation is strongly controlled by fractional crystallization. However, disequilibrium textures suggest  that periodic magma mixing must be significant in producing cyclic chemical variations.