Tectonic evolution of the Andes of Neuquén: Constraints derived from the magmatic arc and foreland deformation

Abstract

The Andes of Neuquén (36°- 38°SL) have distinctive characteristics within the Central Andes inherited from the alternation of periods of generalized extension and subsequent compression. The Loncopué trough, as a result of these processes, is an unique long depression at the foothills parallel to the Principal Cordillera, and consists of a complex half-graben system produced during Oligocene times and extensionally reactivated in the Pliocene – Pleistocene. Its northern sector concentrates the present contractional orogenic front. The nature and volume of the arc-related igneous rocks, location of the volcanic fronts, expansions and retreats of the magmatism, and the associated igneous activity in the foreland, together with the analyses of the superimposed structural styles, permitted to constrain the alternating tectonic regimes. On these bases, different stages from Jurassic to Present are correlated with changes in the geometry of the Benioff zone through time. Period of steepening of the subduction zone are associated with large volumes of poorly evolved magmas and generalized extension. On the other hand, shallowing of the subduction zones are linked to foreland migration of more evolved magmas associated with contraction and uplift in the Principal Cordillera. The injection of hot asthenospheric material from the subcontinental mantle into the asthenospheric wedge during steepening of the subduction zone, produced large melting and poorly evolved magmas in an extensional setting. These periods are linked to oceanic plate reorganizations in the late Oligocene and in the early Pliocene.