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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]

Las Cañas Plutonic Complex (LCPC) is a small representative of the Famatinian Ordovician plutonism (470.4 ± 8.1 Ma) located in the northeastern sector of Sierra Grande de San Luis, Argentina. The LCPC was emplaced into a metasedimentary sequence, which reached their metamorphic climax under high-temperature/low-pressure conditions (∼680 ± 37 °C and 550 ± 120 MPa). The bodies of the LCPC are zoned by rocks of different compositions that represent ultrabasic, basic, intermediate and acidic trends (hornblendites, gabbros, tonalites, and granodiorites). Their petrological, mineralogical and geochemical characteristics indicate that multiple processes formed them, mainly crystal fractionation of magnesian, calc-alkaline and metaluminous magmas (typical of arc), but also different assimilation degrees of crustal melts from the fusion of metawackes involving AFC processes. Fieldwork (structural and petrological data), the geochemical characteristics of rocks [eg. Low Sr/Y and (Gd/Yb) C- N ], and thermobarometric results, indicate a relatively shallow fractionalization for the LCPC, which is in line with a pre-collisional arc stage linked to an extensive retro-arc setting for the Famatinian orogeny in Sierra de San Luis. • A new Ordovician absolute age was determined for Las Cañas Plutonic Complex. • The geology and petrology show that the plutons are composed of several facies. • Geochemical modeling indicates multiple processes for the plutonic rocks origin. • The geotectonic setting during the emplacement of the plutons is discussed. [ABSTRACT FROM AUTHOR]