Mississippian extensional volcanism along the western margin of Gondwana: geochemical and isotopic constraints from the central Andes of Argentina.

MARTINA, F.; ASTINI, R.A.; MANTON, W.; STERN, R.J.

Antofagasta

Congreso; XIII Congreso Geologico Chileno; 2012

Universidad Catolica del Norte

The southern Puna region in NW Argentina records a major volcanic event of Mississippian age. New geochemical data suggest the presence of basalts, trachytes and rhyolites with high total alkali content in the basic and intermediate rocks. LILE content is usually high and REE show LREE-enriched patterns with negative Eu anomalies in the most differentiated rocks. Basalts show HREE depletion suggesting a garnet-bearing mantle source. The Nd isotopic data indicate a depleted mantle source for basalts. The trachytes and rhyolites record varying degrees of crustal contamination but always with contribution from mantle materials. In addition, none of the samples shows evidence of subduction. These data are more compatible with an extensional setting and contrast with observations in Peru and Patagonia. The difference may be explained by changes in the geometry and physical properties of the downgoing slab. According to literature this segment of the Andes coincided with the alleged collision of Chilenia in the Middle Devonian which could have triggered the extension and resulting asthenospheric upwelling by rollback of the Chilenia lithosphere.