Foreland basin deposits associated with Cuyania accretion in La Pampa Province, Argentina

In the province of La Pampa, south-central Argentina, adjacent to the Cuyania–Pampia terrane boundary, a Late Ordovician–Devonian marine foreland basin generated after the Middle Ordovician (Darriwilian) collision of Cuyania has been recognised, and is herein referred to as the Curacó basin. This basin was formed on crust of the Cuyania terrane, immediately to the west of the Pampia terrane. Its fill primarily comprises sandstones and shales of the La Horqueta Formation, unconformably overlain by Permian continental sediments (Carapacha Formation). The extent of the Curacó basin is investigated using aeromagnetic data; its depocentre is conspicuously delineated by a narrow NNW-orientated magnetic low. In addition, scarce outcrops assigned to the same sequence are found on the Pampian continental crust, about 50 km to the east, in the proximity of the Valle Daza estate (Valle Daza sub-basin). The studied marine sequence of La Pampa is equivalent to other Lower to Middle Paleozoic units of the eastern margin of the Cuyania terrane and is clearly distinguished from the overlying Permian continental sedimentary sequence. U–Pb SHRIMP dating of detrital zircons from Valle Daza indicates a maximum deposition age of ca. 466 Ma; the minimum age is given by the intrusion of granites at ca. 405 Ma (i.e. Early Devonian). Geochemical data indicate that the Curacó basin was primarily sourced by an active continental margin, possibly the Ordovician Famatinian arc.