Early Cretaceous Volcanism in Central Argentina

Abstract

The main exposed site of Early Cretaceous volcanism in central Argentina is located in Sierra Chica of Cordoba Province (SCC), within the Central Rift System. Also to the south, in Levalle basin, a thick Early Cretaceous volcanic pile lies buried in the subsurface. Other localities where volcanism is exposed are Sierra de las Quijadas and Cerrillada de las Cabras of San Luis Province. In SCC, as in the other mentioned localities, a volcanic–sedimentary complex was developed under rifting tectonics. Lava flows are frequently associated with scoria fall, pyroclastic and phreatomagmatic breccias within a strombolian-type volcanism. A new 40Ar/39Ar dating performed on sanidine phenocrysts of a trachyte from Almafuerte locality indicated an age of 129 ± 1 Ma. Diverse groups of rocks, mainly of potassic character, were distinguished: (1) alkali basalt—trachyte suite, (2) transitional basalt—latibasalt suite, (3) basanite—phonolite suite and (4) ankaratrites. Magma evolution must have taken place at crustal level(s) from distinct parental melts, mainly through fractional crystallization in an open-system magma chamber. Mantle source composition supports residual garnet and phlogopite, it does not exhibit features related to slab-derived metasomatism despite its location over Pampean mobile belt, and bears a lithospheric nature. SCC volcanism is of high Ti, display similarities with potassic Brazilian localities around Parana basin as Alto Paranaiba and Goias, pointing out analogies in their mantle sources.