We propose an integrated kinematic model with mechanical constrains of the Maipo–Tunuyán transect (33°40′S) across the Andes. The model describes the relation between horizontal shortening, uplift, crustal thickening and activity of the magmatic arc, while accounting for the main deep processes that have shaped the Andes since Early Miocene time. We construct a conceptual model of the mechanical interplay between deep and shallow deformational processes, which considers a locked subduction interface cyclically released during megathrust earthquakes. During the coupling phase, long-term deformation is confined to the thermally and mechanically weakened Andean strip, where plastic deformation is achieved by movement along a main décollement located at the base of the upper brittle crust. The model proposes a passive surface uplift in the Coastal Range as the master décollement decreases its slip eastwards, transferring shortening to a broad area above a theoretical point S where the master detachment touches the Moho horizon. When the crustal root achieves its actual thickness of 50 km between 12 and 10 Ma, it resists further thickening and gravity-driven forces and thrusting shifts eastwards into the lowlands achieving a total Miocene–Holocene shortening of 71 km.

RESUMEN.Los intentos por diferenciar y correlacionar las unidades geológicas en la cordillera Principal Andina, entre 31°30'S y 33°S, se han enfrentado a numerosos obstáculos debido a la monotonía litológica de las potentes secuencias de carácter volcánico que las conforman, la complejidad estructural, la falta de datos geocronológicos que las limiten y la errada consideración inicial de un rejuvenecimiento en las edades radiométricas obtenidas. Las unidades reconocidas al oriente de la zona de Falla Pocuro fueron inicialmente atribuidas al Cretácico (Formación Los Pelambres en Chile y Formación Juncal en Argentina). Esta contribución complementa los trabajos previos mediante un levantamiento geoló-gico-estructural desarrollado entre 32° y 32°30'S, el que, junto a 8 nuevas dataciones U-Pb en circón, permite reconocer niveles del Cretácico Superior (Formación Salamanca) en el sector occidental de la cordillera Principal, subyacentes a rocas cenozoicas de las formaciones Abanico y Farellones. Las unidades cenozoicas a esta latitud se han subdividido en 3 asociaciones de facies vinculadas al volcanismo Oligoceno Superior-Mioceno. Gran parte de la cordillera Principal en esa latitud se compone de estas unidades cenozoicas, hasta el límite oriental del área de estudio (frontera Chile-Argentina). En el sector occidental de la región, la esencialmente volcánica Formación Abanico presenta las facies más proximales con leve deformación, mientras que las unidades más distales, cerca y allende la frontera, se encuentran intensamente deformadas por eventos ocurridos, uno entre 21 y 18 Ma, y otro con posterioridad a 18 Ma. Por otra parte, en las cercanías de la Falla Pocuro, la presencia de afloramientos del Cretácico Superior, discordantemente subyacentes a depósitos oligocenos-miocenos levemente deformados, permiten limitar su período de actividad principal previo al depósito de estos. ABSTRACT. New stratigraphical and geochronological constraints for the Mezo-Cenozoic deposits in the High Andes of central Chile between 32° and 32°30'S: Structural and palaeogeographic implications.Attempts to differentiate geological units of the Andean Principal Cordillera, between 31°30'S and 33°S, faced several problems until very recently. The lack of geochronological data or the equivocal interpretation of some existing radiometric ages from thick volcanic and volcaniclastic sequences, along with their structural complexity and lithologic monotony, obscured the recognition and relationships between units. This made a tectonic interpretation difficult as the units cropping-out on the eastern side of the Pocuro Fault zone were initially assigned to Cretaceous formations (Los Pelambres Formation in Chile and Juncal Formation in Argentina). Structural-geological work carried out between 32° and 32°30'S, together with 8 new U-Pb zircon datings, allowed us to recognize the presence of Upper Cretaceous levels (Salamanca Formation), underlying volcano-sedimentary younger units of Abanico and Farellones formations. The latter were interpreted...

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We use analogue modelling to investigate the response of compressional deformation superimposed on an extensional basin with along-strike changes in width. Parameters described include extension and shortening distribution and directions, orientation of structures and degree of basin inversion. Two types of model are presented: in the first (Type I), an extensional basin is constructed with variable width (applying differential extension) and subsequently inverted by homogeneous shortening; in the second (Type II), an extensional basin with constant width is subsequently inverted by inhomogeneous shortening (differential compression). From our observations, we compare both types of model to structural patterns observed in some natural cases from the Central Andes. Both models generate oblique structures, but in the Type II model a significant rotation is characteristic. Our results suggest that in the Central Andes region between 32° and 33°S, the Abanico Basin may correspond to a basin of smaller area compared to the larger basin south of 33°S. Our Type I model further explains some patterns observed there, from which we conclude that the control exercised by the width of a pre-existing basin should be considered when interpreting the geological evolution of that area of the Andes.