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  • 1
    Publication Date: 2014-02-07
    Description: Isolated marine sedimentary Lower Cretaceous deposits crop out in the foreland of the Neuquén Basin, west-central Argentina. They are the result of an anomalous uplift of the Sierra de Chachahuén in the far foreland region. These outcrops are assigned to the Agrio Formation based on their rich fossil contents. In particular, the study reveals a unique outcrop of continental facies along the eastern proximal margin of the basin that were known only from core wells, and constitutes the first exposed evidence at the surface. These deformed deposits are 70 km from the Andean orogenic front and present 2 km of local uplift produced by high-angle basement reverse faults that reactivated a previous Early Mesozoic rift system. The increase in compression was related to the decrease in the subduction angle. This fact, together with the expansion of the magmatic arc, controlled the Chachahuén calc-alkaline Late Miocene volcanic centre and the uplift of the Mesozoic deposits in the foreland. This broken foreland was associated with localized heating of the Miocene volcanic centre that produced the rising of the brittle-ductile transitions. This fact weakens the foreland area, which was broken by compression during the development of the Payenia flat-slab.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 2
    Publication Date: 2014-08-29
    Description: In this classic segment, many tectonic processes, like flat-subduction, terrane accretion and steepening of the subduction, among others, provide a robust framework for their understanding. Five orogenic cycles, with variations in location and type of magmatism, tectonic regimes and development of different accretionary prisms, show a complex evolution. Accretion of a continental terrane in the Pampean cycle exhumed lower to middle crust in Early Cambrian. The Ordovician magmatic arc, associated metamorphism and foreland basin formation characterized the Famatinian cycle. In Late Devonian, the collision of Chilenia and associated high-pressure/low-temperature metamorphism contrasts with the late Palaeozoic accretionary prisms. Contractional deformation in Early to Middle Permian was followed by extension and rhyolitic (Choiyoi) magmatism. Triassic to earliest Jurassic rifting was followed by subduction and extension, dominated by Pacific marine ingressions, during Jurassic and Early Cretaceous. The Late Cretaceous was characterized by uplift and exhumation of the Andean Cordillera. An Atlantic ingression occurred in latest Cretaceous. Cenozoic contraction and uplift pulses alternate with Oligocene extension. Late Cenozoic subduction was characterized by the Pampean flat-subduction, the clockwise block tectonic rotations in the normal subduction segments and the magmatism in Payenia. These processes provide evidence that the Andean tectonic model is far from a straightforward geological evolution.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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