Somun Curá post- plateau stage: large bimodal complexes, northern Patagonia. Argentina

SALANI, F.;; REMESAL, M.; CERREDO, M. E.

Reykjavík, Iceland

Simposio; IAVCEI 2008 (17 - 22 August). International Association of Volcanology and Chemistry of the Earth´s Interior. General Assembly Reykjavík, Iceland.; 2008

International Association of Volcanology and Chemistry of the Earth´s Interior.

The postshield Barril Niyeu Volcanic Complex (BNVC) is a Neogene eruptive building located at the SW corner of the Oligocene basaltic Somún Curá plateau. The BNVC is made up of pyroclastic and lava facies which span from basaltic through trachyte to minor rhyolite compositions. This paper deals with the petrographic and geochemical characterization of the basaltic lavas of the Complex; three main basaltic groups are distinguished: transitional basalts, alkaline basalts and trachybasalts; the former correspond to porphyric lavas with olivine and plagioclase phenocrysts and display the lowest (La/Yb)N ratio (9.6). The alkaline basalts occur mainly as porphyritic lavas bearing plagioclase, olivine and titanoaugite phenocrysts; intermediate (La/Yb)N ratios (12-14) characterize this group. The last eruptive stage of the BNVC corresponds to the trachybasalts which appear either as lava flows or as spatter cones; rocks display aphanitic textures and the highest (La/Yb)N ratios (14-18) of the basic rocks. Evidences of upper crustal contamination and/or magma mixing processes are common both in alkaline basalts and