Abstract

TOSELLI, Alejandro José; ROSSI, Juana Norma  and  STIPP BASEI, Miguel Angelo. El Complejo Punta Negra - Cerro Negro: un acontecimiento volcanico- plutónico único en el ciclo famatiniano en la zona batolitica central (La Rioja y Catamarca, Argentina). Ser. correl. geol. [online]. 2015, vol.31, n.2. ISSN 1666-9479.

This paper reports the frst occurrence of Ordovician volcanic - plutonic rocks in the Nor-thwestern Sierras Pampeanas of Argentina located at the southeast of the Sierra de Vinquis and in the northern tip of the Sierra de Velasco. They form an exogenous lava dome of medium to coarse - grained dacite, andesite and rhyolite porphyries and local breccias syn-genetically formed, affected by post-emplacement deformation. The Ordovician porphyritic Cerro Negro rocks, with tectonic deformation, show intrusive contacts with banded schists that contain quartz-tourmaline veins with scheelite mineralization, and are intruded by Carboniferous granite in the meta-vulcanites. The Ordovician meta-vulcanites of the Punta Negra, are intruded at the east by a Carboniferous granite, and to the west show tectonic contacts with deformed Ordovician granites. The porphyritic rocks are intruded by late aplitic tourmaline-bearing dikes without ore-bearing mineralization. The meta-vulcanites are composed by quarte, plagioclase, biotite, chlonte, epidote and opaques. Metapelite xenoliths mcluded m the Punta Negra porphyry, show cordiente, biotite and potassium feldspar formed by thermal metamor-phism. Geochemically the both porphyries are calc-alkalme and peralummous. Trace elements geochemistry ís similar to the compositional patterns of Continental Islands Volcanic Are, m transition to Normal Are, that are similar to the composition of the Famatmian vulcanism elsewhere. The mitial valúes of isotopes of Sr 0.7117 - 0.7128 and D Nd of -5.0 - 5.9, indícate a crustal ongin. The Nd model ages obtamed of 1.5 and 1.6 Ga are concordant with those of other Famatmian granites. Both subvolcanic outerops are correlated on the basis of petrographic, geochemical and isotopic similanties and also by the geochronologic age of 481 + 9 Ma ín Cerro Negro, and 471 + 3 Ma for Punta Negra, that are the only known sub-volcanic manifestations ín the Northwestern Sierras Pampeanas.

Keywords : Ordovician.Porphyntic dacites. Calc-alkalme. Northwestern Sierras Pampeanas.

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