Tectonic evolution of the Andean Fold and thrust belt of the southern Neuquén Basin, Argentina

Abstract

The Andean Fold and Thrust belt between 36° and 39°S can be divided in two sectors. The Eastern Sector corresponds to the Agrio Fold and Thrust Belt (FTB) characterized by a major exhumation during the Late Cretaceous, and minor deformation during the late Eocene and Late Miocene. The Western Sector corresponds to the main cordillera and is characterized by a complex evolution that involves periods of out-of-sequence thrusting with respect to the previously deformed outer sector, and pulses of relaxation of the compressive structure. Cretaceous uplift constituted an orogenic wedge that extended to the inner sectors of the Agrio FTB. Eocene compression was mainly concentrated within the Western Sector but may have reactivated the pre-existing structures of the Agrio FTB, such as the Cordillera del Viento. Late Miocene minor compressional deformation occurred in the retro-arc area and extended into the foreland area. This deformation event produced the closure of a short-lived intra-arc basin (Cura Mallín Basin, 25-15 Ma) at the innermost sector of the FTB. The Pliocene and Quaternary, between 37°30′ and 39°S, have been periods of relaxation of the inner part of the FTB and fossilization of the Agrio Fold and Thrust Belt. Localization of episodic late Oligocene-Ear ly Miocene and Pliocene to the present extensional structures in the intra- and inner retro-arc is controlled by pre-existing Jurassic half-grabens related to the formation of the Neuquén Basin. The Jurassic rift seems to be controlled by deep crustal-lithospheric discontinuities derived from a Proterozoic-Palaeozoic history of amalgamation in the area, now deeply buried under multiple episodes of Mesozoic-Tertiary synorogenic and synextensional sedimentation.