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The Famatina System is an elongated geomorphological zone between the Eastern and Western Sierras Pampeanas, characterized by important Ordovician volcanism. The basement consists mainly of a sedimentary protolith, metamorphosed to low grade during the Pampean orogeny (Early-Mid-Cambrian), together with sparse outcrops of highgrade metamorphic rocks. Overlying this basement, the Volcancito Formation consists of thin sediments of uppermost Cambrian and Tremadocian age, deposited in restricted basins. A much more voluminous series of volcanic and sedimentary deposits, initiated in the Arenig and culminating in Early-Mid-Llanvirn times, indicates a significant increase in the rate of tectonic subsidence. The form of these deposits shows that they were laid down in an ensialic marginal basin that developed contemporaneously with active volcanic activity. The products of the latter were predominantly acidic, generated by crustal anatexis, with much rarer occurrence of basaltic and trachyandesitic compositions. The volcanic rocks are cut by granitoids of unknown absolute age, although the few radiometric ages obtained on them do not exceed 460 Ma. The volcano-sedimentary basin is interpreted as related to subduction, and the granitic and volcanic rocks together represent a continental magmatic arc developed regionally during the Early Ordovician.

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