THE NEOGENE BARRIL NIYEU VOLCANIC COMPLEX. SOMÚN CURÁ MAGMATIC PROVINCE. NORTHERN EXTRA ANDEAN PATAGONIA. ARGENTINA

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

BOLLETTINO DI GEOFISICA TEORICA ED APPLICATA

ISTITUTO NAZIONALE DI OCEANOGRAFIA E DI GEOFISICA

Lugar: Trieste; Año: 2010 vol. 51 p. 85 - 88

0006-6729

The most voluminous post-plateau volcanic field is the Lower Miocene (20-18 Ma) Barril Niyeu Volcanic Complex (BNVC), which was built through several stages of both effusive and explosive activity outpoured from at least five emission centres (presently cauldrons, ranging from 2 to 5 km in diameter) and of distinct trachyte/rhyolite and basaltic compositions. The final basaltic stage is dominated by lavas, although minor breccia and clastogenic facies and spatter cones also occur. Local variations from this general stratigraphic scheme exist, which suggest a certain synchronism of different composition events related to distinct vents. The bulk of the complex is formed by porphyric trachyte lavas (bearing sanidine and aegirine, aegirine/augite phenocrysts set in a trachytic groundmass) and comendite or quartz-trachyte lava domes within the cauldrons. Although several trachyte groups were dintinguished all share a peralkaline character, as is common in other post- Somún Curá plateau Neogene complexes. The BNVC (as well as other Early Miocene bimodal complexes) was built when a dramatic plate reorganization process hadtaken place along the pacific margin.We propose that the partial melting of the Patagonian asthenosphere was triggered both by this drasticgeodynamic change as well as by the dehydration/partial melting processes underwent by foundered Aluk plate. Therefore, the arc-like signatures of some inter-elemental ratios would be related to the detached slab and not to the influence of a contemporaneous arc.