Resumo

ARMAS, Paula et al. Caracterización de las facies volcano-sedimentarias de la formación Chuschín, sector sur- occidental del sistema de Famatina, provincia de La Rioja. Rev. Asoc. Geol. Argent. [online]. 2016, vol.73, n.1, pp.78-92. ISSN 0004-4822.

The Chuschín Formation is a volcano-sedimentary succession that is found in the south-western section of the Famatina System and its genesis is linked to the evolution of the Western margin of Gondwana during the Lower and Middle Ordovician. Facies analysis carried out in the Chuschín Formation allows characterizing the nature of volcano-sedimentary deposits and understanding some process of volcanism and sedimentation in this part of the Famatinian magmatic arc. The volcano-sedimentary succession includes three coherent volcanic facies: massive rhyodacite, banded rhyolite and massive rhyolite with spherulitic texture. Volcaniclastic facies are divided into autoclastic, pyroclastic, and volcanogenic deposits. Several rocks including hyaloclastic breccia, lapilli tuffs, vitrophyric tuffs, massive monomictic breccia, massive polymictic breccia and tuffaceous sands are recognized within the volcaniclastic facies. Epiclastic facies occur in subordinate abundance and are characterized by alternating laminated metagreywacke with massive and laminated metasiltstone. Lithological diversity and facies association in the Chuschín Formation reflect several events of silicic eruptive volcanism mostly emplaced under sub-aqueous conditions associate with explosive volcanism. The main characteristics of eruptive and explosive volcanism inter-stratified with volcaniclastic deposits suggest that these rocks were sourced from a nearby volcanic edifice. Whereas, epiclastic facies are material deposited fall-out and sedimentation by turbidity currents in low energy environments.

Palavras-chave : Coherent volcanic and volcaniclastic rocks; Facies analysis; Lower and Middle Ordovician; Famatina System; La Rioja province.

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