Role of basin width variation on the development of inverted structures: Insight from analogue modelling and implications for the Central Andes

JARA PAMELA; LIKERMAN JEREMIAS; WINOCUR, DIEGO; GHIGLIONE MATÍAS; CRISTALLINI ERNESTO; PINTO LUISA; CHARRIER REYNALDO

Córdoba

Congreso; XIX Congreso Geológico Argentino; 2014

Asociación Geológica Argentina

Our modelling is inspired in contributing a better understanding of factors that control some latitudinal variation in strikes of structures and the evolution of the Central Andes. The study region corresponds to the High Central Andean between 32° and 34° S. South of 33° S, many studies recognize that Abanico Formation?s (Eocene-Miocene) volcanic rocks were deposited in an extensional basin over 50 km wide, with a ~ N-S orientation and high subsidence rates, with some depocenters reaching more than 3.5 km in depth (ver Fock et al. 2005; Charrier et al. 2002, 2007; Farías et al. 2010), subsequently inverted (Miocene). North of 33° S, new field-based data indicate that distal facies of this formation, which outcrop in the eastern side of the Principal Andean Cordillera at this latitude, accumulated in a basin less than 10 km wide with an estimated thickness of about 3.0 to 3.5 km (Jara & Charrier, 2014). In order to study the role of the extensional basin width has over subsequent superimposed compressive structures and their trend, two main types of models were configured to study the effect of two principal variables: Type I, homogeneous shortening on variable basin width; and Type II; inhomogeneous shortening (differential) over a constant-width pre-existing basin. In the Type I model, compressive structures with uplift concentrated on a narrow area developed on the sector with smaller amounts of previous extension. In the region with greater extension, the compressive deformation was accommodated between the boundaries of the extensional basin, occupying a wider area, with consequent lower rising structures and topography. Furthermore, these latitudinal differences of uplift between the northern and southern zones played an important role in the obliquity of compressive structures. The model shows that NNW-trending structures are generated in the narrower basin region to the north, which is consistent with a ~10 km wide area of active depocenters during the Oligocene-lower Miocene at ~ 32°10´ S, compared to the region south of 33° S, where the basin would have been over 50 km wide. This results suggest that the curvature of the La Ramada fold and thrust belt may be influenced by a stronger and narrower uplifting north of 33° S, compared to smaller and wider uplift south of 33° S. In the Type II model with equal basin width and subsequent superimposed differential compression, the basin did not control the strike of the compressive structures. Conversely, regional structure is controlled by the rotation during the shortening phase, which generates the greatest amount of folds and faults and greater uplift in the most compressed area. Thus, the Type II model can explain the development of oblique structures, but it needs an important oroclinal rotation, which is not consistent with geological observations of the studied region. The experimental models developed show that the control exerted by the width of a pre-existing basin, which was subsequently reversed, has important implications in the resulting structural pattern, and should be considered when interpreting the geological evolution of an inverted natural basin.