Abstract

ESCOSTEGUY, Leonardo  and  FRANCHI, Mario. Stratigraphy of the Chapelco region, province of Neuquén. Rev. Asoc. Geol. Argent. [online]. 2010, vol.66, n.3, pp.418-429. ISSN 0004-4822.

A regional geological mapping in the Chapelco range area (Neuquén) is presented. Several volcano-sedimentary units are distinguished, related to the Cenozoic arc magmatism. The Huitrera Formation (Paleogene) is the oldest one covering the crystalline basement of the Colohuincul Complex. It constitutes the base of the Chapelco range, and it is locally associated to sedimentary rocks and basaltic flows of the Lolog Formation in the Chimehuín River area. The following cycle is composed by the mid-Miocene pyroclastic Collón Cura Formation, in the homonymous river, covered by epi- and pyroclastic deposits and basalts of the Caleufú Formation (mid-Miocene to lower Pliocene). Pliocene magmatism in the area is represented by basalts of the Tipilihuque Formation, and possibly by acidic subvolcanic stocks of Los Pinos Formation which intrudes Caleufú Fm. As a further record of Pliocene volcanism, we propose in this paper the basaltic and andesitic flows of Chapelco Formation, which compose the upper levels of Mount Chapelco. The Chapelco flows were considered by some authors as Paleogene in age. However, they unconformably overly the Huitrera Formation; as it is seen in the western slope of the Chapelco range. To the east, in the headers of Quemquemtreu River, they cover the Miocene-Pliocene Caleufú Formation. Two K/Ar ages were obtained for Chapelco Formation: 4,8 ± 0,3 y 3,7 ± 0,3 Ma (Pliocene). These flows are followed in the Mount Puntudo Grande by a basaltic volcano keeping its conical form, made up on rocks of the Chapelco Formation. The Chapelco range is therefore composed by three volcanic units: Huitrera Formation (Paleocene), Chapelco Formation (Pliocene) and Cerro Puntudo Grande Basalt (Pleistocene).

Keywords : Cordillera Patagónica; Stratigraphy; K-Ar dating; Ceinozoic; Neuquén.

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