Abstract
The Agrio fold and thrust belt is a thick-skinned orogenic belt developed since Late Cretaceous in response to the convergence between the Nazca and South American plates. The integration of new structural field data and seismic line interpretation allowed us to create two balanced cross-sections, which help to analyse the geometry of both thick and thin-skinned structures, to calculate the tectonic shortenings and finally to discuss the main mechanisms that produced this fold and thrust belt. The predominantly NNW-SSE structures show varying wavelengths, and can be classified into kilometer-scale first order basement involved structures and smaller second, third and fourth order fault-related folds in cover rocks with shallower detachments. Thick-skinned structures comprise fault-bend folds moving into the sedimentary cover, mainly along Late Jurassic evaporites, which form basement wedges that transfer the deformation to the foreland. Thus, shortenings in both basement and cover rocks must be similar and consequently, by measuring the contraction accounted for thin-skinned structures, is possible to propose a suitable model for the thick skinned deformation. The balanced cross-sections indicate shortenings of 11.2 km (18%) for the northern section and 10.9 km (17.3%) for the southern section. These values are different from the shortenings established by previous works in the region, reflecting differences in the assumed model to explain the basement-involved structures. According to our interpretation, the structural evolution of this fold and thrust belt was controlled by major basement-involved thrust systems with subordinate influence of inversion along pre-existing normal faults during the Andean compression.
Highlights
The Agrio fold and thrust belt (Ramos, 1978) is part of the Southern Central Andes and it is located at the Central-Western region of Argentina (Fig. 1a)
The Agrio fold and thrust belt is a thick-skinned orogenic belt developed since Late Cretaceous in response to the convergence between the Nazca and South American plates
After testing with different values for these parameters, we found that the geometry and kinematics of the folds in Loma Tilhué can be adequately explained using a trishear apical angle of 60° and a p/s ratio of 2
Summary
The Agrio fold and thrust belt (Ramos, 1978) is part of the Southern Central Andes and it is located at the Central-Western region of Argentina (Fig. 1a). The region of study is located in the Neuquén Basin, which is one of the most important oil producing sedimentary basins of Argentina In this zone, several works on the stratigraphy and the structure have been conducted because of the scientific and economic interest due to the presence of hydrocarbon deposits (Groeber, 1929, 1946; Zöllner and Amos, 1973; Minniti et al, 19861; Gulisano and Gutiérrez Pleimling, 1995; Vergani et al, 1995; Kozlowski et al, 1998; Zapata et al, 1999; Zapata and Folguera, 2005; Leanza et al, 2006; Zamora Valcarce et al, 2009; Rojas Vera et al, 2015; Turienzo et al, 2014, 2018; Sánchez et al, 2014, 2015). Thick-skinned structures have been recognized in the outer zone from seismic subsurface information (Zapata et al, 2002; Zamora Valcarce et al, 2009)
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