Time constraints on the Early Palaeozoic docking of the Precordillera, central Argentina

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Abstract
40 Ar/ 39 Ar incremental-release ages have been determined for muscovite and hornblende concentrates prepared from basement rocks of the Sierra de Pie de Palo, in the western Sierras Pampeanas, east of the Early Palaeozoic Precordillera. The basement is mainly represented by variably metamorphosed units, including ophiolites, orthogneisses and schists. Previous U-Pb, Rb-Sr, K-Ar, and 40 Ar/ 39 Ar dating of magmatic and metamorphic zircons from the basement has indicated a Middle Proterozoic age. The 40 Ar/ 39 Ar plateau ages constrain a series of ductile deformational events that are correlated with development of structural discontinuities in adjacent foreland basins. The following deformational events are postulated: (1) initiation of collision and drowning of the Precordillera platform against Gondwana (470–460 Ma); (2) flexural extension associated with normal faulting due to tectonic loading of the Gondwana margin; and (3) development of a foreland basin (450–430 Ma). These Mid-Ordovician-Silurian events were related to collision of several exotic Early Palaeozoic terranes along the Gondwana margin. The Punta Negra foreland basin developed further west during Early to Mid-Devonian (410–380 Ma) times, and was linked to the beginning of the docking of the Chilenia terrane along the western margin of the Precordillera.