Abstract

BARRIONUEVO, Marcelo; ARNOSIO, Marcelo  and  LLAMBIAS, Eduardo J.. New geochronological data from subsurface and outcrops of the Choiyoi Group in the west of La Pampa: Stratigraphic implications. Rev. Asoc. Geol. Argent. [online]. 2013, vol.70, n.1, pp.31-39. ISSN 0004-4822.

New geochronological information from subsurface rocks of 25 de Mayo - Medanito S.E. oilfield and surface rocks from Colón hill, located to the southwest and west-central of La Pampa province and 135 km distant from each other, is published. Samples from both outcrops and hydrocarbon well cores drilled at the top of the volcanic unit are rhyolitic ignimbrites, with medium to high degree of welding. 3D seismic analysis shows that three out of four subsurface samples correspond to the top of halfgraben filling, with strike direction 100°, whereas the fourth corresponds to units that overlap the halfgraben. Outcrop samples are outside the Neuquén basin. Five U-Pb single zircon ages average 246 Ma for the top of the filling of halfgraben, whereas the sample that overlaps the halfgraben yielded 211 Ma. At cerro Colón four U-Pb single zircon ages average 261 Ma. In this paper rocks from cerro Colón and subsurface rocks from top of halfgraben fill are interpreted as belonging to Upper Section of Choiyoi Group, whereas the sample overlapping the halfgraben would indicate final part of Choiyoi volcanism ("posthumous" volcanism) within Precuyo Cycle.

Keywords : Volcanism; Sinrift; Postrift; Choiyoi; Precuyo; Neuquén Basin.

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