Structural and tectonic assessment of the western Huincul High, Neuquén Basin (Argentina)—The role of structural inheritance and mechanical stratigraphy in inversion systems

Abstract

The Neuquén Basin is a major Mesozoic sedimentary depocentre located in the retroarc foreland of the Argentinian Andes. The basin hosts world renowned inversion systems that have been the target of georesource exploration for the last three decades. The Huincul High is a structurally and economically prominent ca. 270 km long, E–W trending feature that formed by the accretion of exotic Palaeozoic terranes, influencing subsequent Mesozoic deformation in the basin. Exploration in the Huincul High has been mainly focused on the shallow part of the inversion structures leaving a limited understanding of the deep structural architecture and early tectonic evolution, particularly in the western reaches of the high. This research reveals that Late Triassic extensional faulting was followed by widespread thermal subsidence in the Early Jurassic, as shown by the occurrence of an extensive ca. 60 km long, ca. 20 km wide, NE–SW‐trending, central depocentre. In the Early Jurassic, as contraction ensued across this regional sag basin, atypical inversion geometries were developed. These exhibited prominent thickening in the hanging‐wall and, strikingly, in the footwall of reactivated faults. The style of inversion was also markedly influenced by the mechanically weak stratigraphy of the thick, Lower Jurassic, Los Molles formation that promoted broad inversion folding, inhibited shortcut fault creation, and decoupled post inversion deformation from earlier faulting. Quantitative fault analysis suggests that the reactivated faults originated during the Late Triassic extensional phase as separate ca. 10 km long fault segments. The analysis also indicates that segmentation of extensional faults, as well as their orientation to the later contractional vector (SH), spatially dictated style and magnitude of inversion. This research highlights the critical role played by structural inheritance and mechanical stratigraphy in the development of inversion in the Neuquén Basin, which might be of relevance for characterising inversion systems elsewhere. This research also proposes an evolutionary model for the western reaches of the Huincul High that suggests crustal weakening and thermal sag in the Early Jurassic. Moreover, the model highlights a previously unknown late Early Cretaceous transtensional phase that overprints the main Early Jurassic–Early Cretaceous inversion.