Abstract

FRANCO, Jose Alejandro et al. U-Pb LA-ICP-MS zircons ages from sandstones of San José Formation in Ciudad de Piedra and Mesoproterozoic gneisses from Guaviare, Colombia. Bol. geol. [online]. 2022, vol.44, n.3, pp.15-37.  Epub Nov 21, 2022. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v44n3-2022001.

Here we describe part of the single geomorphology at the south of the San José del Guaviare, where low elevation plateaus made of sandstones and undergone by karst processes forms Ciudad de Piedra following (NE-SW - NW-SE) trends. The sandstones belonging to the Ciudad de Piedra Basal Member of the San José Formation contain ichnofossils and petrographically, a predominance of quartz of rounded medium grain is observed and cemented by silica giving greater resistance, over the remaining 5% that corresponds to metamorphic and volcanic lithics, feldspars, micas, opaque and zircons. U-Pb LA-ICP-MS analysis in these zircons showed Proterozoic ages with peaks between 1000 to 1800 Ma, while zircons extracted from a gneiss near Cerritos-El Capricho revealed a concordant age of 1317+4 Ma, interpreted as the age of the protolith. The data obtained confirm that the crystalline basement in the study area belongs to the Amazon Craton and that the sediments that forms the sandstones of the San José Formation, come from this basement composed mainly of gneiss and granitoids. Later, the basement would be intruded by the Nepheline Syenite of San José of Guaviare (~602 Ma), which outcrops in faulty tectonic contact with the San José Formation near Ciudad de Piedra.

Keywords : Geology landscape; Ciudad de Piedra; Provenance; U-Pb Age; Zircon.

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