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Geoacta

versión On-line ISSN 1852-7744

Resumen

LAGORIO, Silvia Leonor  y  VIZAN, Haroldo. El volcanismo de Serra Geral en la provincia de Misiones: aspectos geoquímicos e interpretación de su génesis en el contexto de la Gran Provincia Ígnea Paraná-Etendeka-Angola. Su relación con el volcanismo alcalino de Córdoba (Argentina). Geoacta [online]. 2011, vol.36, n.1, pp. 27-53. ISSN 1852-7744.

In the present paper new geochemical data from Serra Geral basalts of Misiones province are shown. These data are complementary of those previously published for the Large Igneous Province (LIP) Paraná-Etendeka-Angola (PEA). The volcanic rocks from Misiones are tholeiitic of high- and low-Ti varieties; the coexistence of both types in the present sampling, agrees with the fact that this area belongs to the central and southern regions of the Paraná Magmatic Province. Paranapanema, Ribeira, Gramado, Pitanga and Urubici varieties were recognized, being the former the most abundant in the collected rocks. Urubici type sample, from San Ignacio area, is the most occidental expression of this variety in the region. Chemical data point out that magmas of high- and low-Ti were originated from different sources, and evolved through fractional crystallization under low pressures conditions, involving significant crustal contamination only in Gramado magma type. Heterogeneity in the magma, on small and large scales, is in agreement with a subcontinental lithospheric mantle source, where no elements from the called plume Tristan had been recognized. Geochemical data of tholeiites from Misiones and from the whole PEA LIP point out that previous subduction processes (e.g. Transamazonian, Grenvillian and Brasiliano Precambrian Events) must have affected the mantle source of the Cretaceous magmas. The great hotness involved in mantle melting might correspond to a thermal blanketing caused by an ancient supercontinent as Pangea. The location of the main melting zone must have been determined by the effects of the hot uprising limb of a possible large scale convection that would have affected zones of cortical fragility (e.g. sutures between ancient cratons).  On the other hand, volcanism of the sierra Chica de Córdoba (SCC), pratically coeval with that of the PEA LIP, is alkaline of high-Ti and display a peripheral location (64º W; 30º30' - 32º30' S) in relation with the great caloric energy mentioned above. This is consistent with the involved lower melting degrees of the volcanism of SCC respect to those of PEA LIP. Melting could have been triggered by a small scale process called edge-driven convection because of the thickness contrast between Rio de la Plata Craton and Pampia terrane.

Palabras llave : Volcanismo; Cretácico; Misiones; Paraná; Córdoba.

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