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During the Mesozoic, a series of back-arc basins formed along much of western South America. The Neuquen basin, an important petroliferous basin in west-central Argentina, is a roughly triangular remnant of this back-arc basin system preserved along the east side of the Andean Cordillera from about 34° to 40°S. The west flank of the Neuquen basin is formed by the Late Cretaceous-Tertiary foreland fold and thrust belt of the eastern Andean foothills that trends approximately north-south and crosscuts extensional trends that were active during formation of the Triassic-Early Cretaceous Neuquen basin.
Field studies have shown that the style of surface structures varies along the west flank of the Neuquen basin, largely as a result of the changing stratigraphic section in which the structures are developed. In thick sediments of the deeply subsided basin, low-angle thrusting is important, with major decollement in evaporitic and shale intervals. These thrusts show a characteristic ramp and flat geometry. Where the fold and thrust belt crosses a block-faulted Jurassic basin margin, a complex zone of imbricate thrust structures is developed. This structural style is suggested to be due to thrust ramping at the eastern pinch-out of major decollement zones. Where the foothills cross a portion of the eastern platform, the structural style is strongly controlled by sub-Jurassic igneous an metamorphic basement, including compressional reactivation of normal faults formed during Triassic-Jurassic extension. A series of length balanced cross sections shows this variation in structural style.
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