Geochronology and facies analysis of subaqueous volcanism of lower ordovician, Famatinian arc, Argentina.

The Chuschín formation is a sedimentary-volcanic succession of the Famatina System subduction-related arc magmatism. This formation developed along the western margin of Gondwana during the early and middle Ordovician. The interpretation of the Chuschín formation is significant for the understanding of the Famatinian arc. This study provides a detailed facies analysis, which allows characterizing the deposits as well as defining some of the characteristics of the volcanism and sedimentation. Coherent, autoclastic, peperitic, pyroclastic and volcaniclastic facies were recognized between the different volcanic facies. The characteristics and relationships between these facies indicate events of effusive subaqueous volcanism as well as explosive volcanism showing predominantly high temperature features. Both types of volcanism are interbedded with volcanogenic deposits and epiclastic sediment that are associated mainly with turbidity currents. The magmatic and volcanic rocks are dominantly subalkaline, weakly peraluminous and silicic. Two new U-Pb zircon crystallization ages on volcanic rocks from the Chuschín Formation show that this section of the Famatinian arc formed between 463 and 469 Ma (Middle Ordovician). [ABSTRACT FROM AUTHOR]