CUYANIA TERRANE AND THE THICK-SKINNED BELT OF THE FRONTAL CORDILLERA, WESTERN ARGENTINA: STRATIGRAPHIC RELATIONSHIP AND PALEOGEOGRAPHIC SIGNIFICANCE

Metamorphic rocks of Grenvillian age, are exposed in both the San Rafael and Las Matras blocks, and in the Frontal Cordillera. The unexposed basement of Precordillera is known from xenoliths of Grenville age in Miocene volcanic rocks. Ultramafic complex and granulite of Late Precambrian to Early Paleozoic age, have been described in Precordillera and Frontal Cordillera. Siliciclastic marine rock of the La Horqueta Formation crops out in the San Rafael block and in the southern Frontal Cordillera. Similar rocks assigned to the Ciénaga del Medio Group, intercalating pillow basalts of Devonian age, crops out in the Western Precordillera and Frontal Cordillera. Silurian and Devonian sedimentary rocks are widely distributed in Central Precordillera, but their record it is not well constrained in Western Precordillera, except by the Cienaga del Medio Group. Recently, the Los Sombreros Formation has been reinterpreted as a Lower Devonian olistostrome succession, which correlate with the Rinconada Formation, which provide a new insight for the evolution of the Precordillera. In this model, part of the Western Precordillera and the eastern belt of the Cordillera Frontal, formed the Western high that bounded the Los Sombreros basin to the west. The Central Precordillera block and the Western high were the source providing the material infilling the Los Sombreros basin. The huge blocks of metamporhic rocks included in such olistostrome are thought incoming from the Frontal Cordillera, and the huge carbonate blocks of Cambrian-Early Ordovician age, are considered coming from the Central Precordillera. The both Los Sombreros and Rinconada basin are thought as extensional basins controlled by dextral slip, closed with the Chánica tectonic phase, followed of up-lifting, and post-tectonic plutonism. On the basis of these data, it seems reasonable to considerer the eastern belt of the Frontal Cordillera as part of the Cuyania terrane during the Early Paleozoic time.