Abstract

CISTERNA, Clara Eugenia; COIRA, Beatriz  and  DECIMA, Fernanda. Subaqueous eruptions in the Ordovician volcanic arc in the northern Famatina System. Rev. Asoc. Geol. Argent. [online]. 2010, vol.66, n.1-2, pp.225-237. ISSN 0004-4822.

The volcanic - sedimentary sequence studied, exposed along the 27°47`00" - 27°49`18" S and 68°04`52" - 68°02`27" Win the sierra de Las Planchadas, northern Famatina System, records the evolution of an Ordovician volcanic arc. The main volcanic members are basaltic and dacitic lavas and significant volumes of lava-derived clastic aggregates that are produced by quench fragmentation and gravitational collapse. Fragmented lavas, autobreccias and hyaloclastites are valuable indicators of the effusive volcanism under subaqueous conditions. The sequence, including debris-flows and turbidity-current levels, especially at the upper levels of the column, may have developed as a result of repeated syn-volcanic sedimentation events. The fossil content in the volcanogenic facies and levels with pyroclastic clasts and accretionary lapilli reflect a shallow water depositional environment. An exclusive volcanic provenance was recognized even in the epiclastic deposits, pointing to a continuous magmatic activity of the arc and an intermittent intrabasinal contribution related to the instability events. The very high proportion of volcaniclastic deposits in the sequence, especially at the upper levels, indicates an efficient fragmentation processes as well as repeated erosion events during the evolution of the Ordovician basin.

Keywords : Subaqueous volcanism; Arenig; Sierra de Las Planchadas; Famatina System; Argentina.

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