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The hinterland zone of the North Patagonian Andes between 41° and 43°S constitutes a poorly explored sector of the Andes, where no structural studies and scarce geochronological determinations have been carried out. This paper focuses on two isolated volcanic sections hosted at the main Andes, in which field evidence indicates a common synextensional origin. Geochronological data establish that this volcanic event occurred diachronously at the innermost sector of the evolving fold and thrust belt, during middle to late Miocene times. Therefore, the event was briefly coeval and postdated compressive tectonics recognized in the deformational front and correlative to the last phase of pluton emplacement of the North Patagonian Batholith. Local-scale topographic swath profiles performed in this work reveal negative topographic anomalies where normal faults were recognized. Moreover, regional swath profiles show not only a conspicuous depressed zone at the hinterland zone, where the studied sections are located, but also anomalously high altitudes at the foreland zone. In addition, calculated orogenic volumes increase in this sector of the fold and thrust belt, which agrees with recent shortening estimations. These topographic along-strike variations, in association with late Miocene extension following the main compressive stage in the area, are explained by a supercritical stage of the orogenic wedge that would have led to focused extension at the innermost sector of the fold and thrust belt. [ABSTRACT FROM AUTHOR]

The Neogene Penitentes basin registers the earliest synorogenic infill in an inner region of the southern Central Andes, between Principal and Frontal cordilleras at 33°S, which contrast with other Neogene basins that are distributed to the east, in the foreland area. In this work, we focused on the study of the first infill of the basin, the Penitentes Conglomerate, which crops out along the Aconcagua fold-and-thrust belt (Principal Cordillera). We carried out sedimentological, geochronological, and structural studies to better understand the genesis and evolution of these synorogenic deposits. We recognized the Penitentes Conglomerate at the Blanco river and the Potrero Escondido creek, located to the south of the previously established boundaries of the basin. We obtained a maximum depositional age of 15 ± 1 Ma (weighted mean 206Pb/238 U age; n = 8; MSDWD = 4.5; error of 95% conf.) for the base of the Penitentes Conglomerate in the Potrero Escondido creek. Based on clast composition and U-Pb detrital zircon ages of the Penitentes Conglomerate base, the provenance analysis reflects the Aconcagua's fold-and-thrust belt exhumation to the west of the basin. The denudation processes that affected the Principal Cordillera generated an unroofing sequence within the Penitentes Conglomerate. In contrast, towards the top of the sequence, the Penitentes Conglomerate has sediment input derived from eastern sources, which indicates that the Frontal Cordillera was exhumed and acted as a sediment source area for the Penitentes basin by the Middle Miocene (~14 Ma). In this sense, the chronology of the uplift of Principal and Frontal cordilleras agrees with the east-vergent orogenic model for the Andes. The structural analyses presented in this paper show a minimum shortening of 62% for the Aconcagua fold-and-thrust belt with an out-of-sequence deformational phase during the mid-late Miocene, after the uplift of the Frontal Cordillera. • We determined the southern extension of the intermontane Penitentes basin. • A maximum depositional age of 15 Ma was obtained for the first synorogenic infill. • The Principal and Frontal cordilleras were source areas for the Penitentes basin. • Our studies show that the Frontal Cordillera was uplifted by the middle Miocene. • The Principal Cordillera had a final contractional pulse at the late Miocene. [ABSTRACT FROM AUTHOR]

Abstract: The structure and tectonics of the retro-arc area of the Andes between 38°30′ and 40°S remains poorly understood because of the scarcity of previous structural studies. This paper analyzes the styles, distribution and timing of the deformation in the eastern flank of the Andes between these latitudes, with focus in the Tertiary tectonics of the area. This Andean section can be divided into an internal and an external domain based on its distinctive structural evolution. The boundary between them coincides with the Bio Bio and Aluminé valleys, which separate sectors of the fold-and-thrust belt with opposite vergence and different structural styles. Structures developed in the external domain during the Andean cycle are associated with a west-verging fold-and-thrust belt which was controlled geometrically by pre-existing normal faults of the Mesozoic rift phase. We also differentiate three segments along the external domain of the inner retro-arc zone at these latitudes. Each segment is associated with a Tertiary depocenter related to the western border of a structural high (Copahue–Pino Hachado Block and Cordilleras de Catan Lil and Chachil) which constitutes an outstanding feature within the study area. The recognition and interpretation of the main structures and the spatial and temporal distribution of the Tertiary sequences allowed us to establish a tectonic model in which the uplift of this NNW-trending block during upper Miocene times, originated a series of intermontane depocenters well represented between 38 and 40°S. As a result of that, syntectonic and synorogenic deposits accumulated in a compressive regime. These depocenters can be integrated in a narrow deposition zone associated with the western slope of the Copahue–Pino Hachado Block and its southward prolongation in the Cordillera de Catan Lil and Cordillera del Chachil. On the basis of tectonostratigraphic controls we define the last Andean contractional phase of the inner retro-arc area at these latitudes, between 11 and 5.67Ma for the northern segment, between 10 and 6.2Ma for the central segment and between 13 to 8 and 4.3Ma for the southern segment. After this short-lived compressional stage, deformation migrated to the west associated with the onset of the Liquiñe-Ofqui strike-slip fault zone along the intra-arc zone. [Copyright &y& Elsevier]

Abstract: We discuss in detail all the comments made by Petrinovic et al., showing that these are not pertinent to the aim of our study, or based on incomplete information of fault kinematics, or unsupported. Despite our limited amount of data, not any of the raised arguments can be seriously taken into account to alter the proposed scenario. Therefore, we demonstrate that our paper is neither “largely speculative” nor “contains major flaws”. In particular, the limited evidence of pre-Miocene deformation on a part of a proto-Eastern Cordillera does not affect our interpretation. In fact, our aim was not to reconstruct the tectonic history of Eastern Cordillera, identifying any pre-Miocene episode. Rather, it was to define the kinematics of the largest structures affecting its recent evolution. Therefore, the interesting structures described by Petrinovic et al., also kinematically poorly constrained, cannot give useful insights, simply because the aim and time frame of our study are different. [Copyright &y& Elsevier]

Abstract: In this paper we analyse two end-member models of temporal and spatial interactions between thick- and thin-skinned structures in a thrust front with pre-existing rift structures. In the most commonly accepted model, a hinterland-to-foreland sequence of inversion of pre-existing normal faults is proposed. As a result, the emplacement of shallow thrust sheets in the sedimentary cover occurs before the basement inversion in the foreland. In the other model, basin inversion occurs early in the deformation history of the external part of a fold-and-thrust belt, as the result of a foreland-to-hinterland sequence of inversion. The Malargüe fold-and-thrust belt (34–36°S) formed in response to compression of the Mesozoic Neuquén basin during Neogene to Pleistocene times. Integrating detailed structural data from the northern part of this belt with new Ar/Ar dating, we propose a revised kinematic model of thick- and thin-skinned interaction and define the temporal-spatial evolution of the belt. Comparison of the timing of deformation in the thick- and thin-skinned areas strongly supports the hypothesis that the reactivation of normal faults was coeval with the insertion of shallow detachments and low-angle thrusting along the migrating front of the thrust belt and occurred from the foreland to the hinterland. Detachments occur at several stratigraphic horizons, including a deep basement decóllement related to the basement-involved thrusting and shallow detachments located within the Jurassic and Cretaceous beds. These shallow and deep detachments were coeval producing simultaneous development of thrusts during the complex deformation of the thrust front between 15 and 8 Ma. [Copyright &y& Elsevier]