Structural styles of the Villa Unión-San Isidro basement-involved fold and thrust belt, northern Ischigualasto-Villa Unión Basin province of La Rioja, Argentina

Abstract

This chapter focuses on the structural styles of the Villa Unión-San Isidro basement-involved fold and thrust belt in the northern Ischigualasto-Villa Unión Basin of the western Sierras Pampeanas, La Rioja Province, Argentina. The region is situated within the Pampean flat-slab subduction segment (28°–32°30′S) of the Central Andes, and it records the Neogene phase of the Andean orogeny through many basement-involved structures, such as analyzed in this chapter. Detailed seismic interpretation of two poststack time migrated seismic reflection profiles indicates the presence of three WSW–ENE to SW–NE-trending and SE-vergent reverse and thrust blind faults that generate fault-bend folds and fault-propagation folds. In addition to these structures, roughly S–N trending imbricate fault-bend folds contribute to the overall structural grain of the region, which are closely related to thin-skinned faults. The geometry and kinematic of the structures is unraveled based on field work, time-depth conversion of the seismic profiles, implementation of fault-related fold models, and the analysis of Mio-Pliocene growth-strata sediments. We hypothesize that the diverse structural styles and kinematics of folds and faults, as well as their mutual spatial and angular relationships, are strongly suggestive of the influence of preexisting discontinuities in the Proterozoic metamorphic-igneous basement. In addition, this suggests that one or more other episodes of deformation probably developed jointly within a complex but generally synchronous strain field, which, in turn, influenced the Andean tectonic evolution in the region during the Neogene.