Structural Geology: Tectonic History, Macrostructures, Regional Fault Map, Fault Systems, Second-Order Structures, and Impact of the Inheritance

Abstract

Abstract The present-day structure of the Neuquen Basin is the result of the deformation of the sedimentary column through a poly-episodic tectonic history. The initial stage was dominated by extension with a general northeast-southwest direction during the Early Jurassic. The resultant structures were a widespread distribution of northwest-southeast striking grabens and half-grabens defined as the Rift stage. Subsequently, different stages of convergent tectonics took place with different directions of convergence vectors, reactivating and inverting the previous extensional structures and creating new ones. The most important stages were the Aluk stage (Early Jurassic-Early Cretaceous), the Farallon stage (Cretaceous), and the Nazca stage (Cenozoic). The tectonic pulses produced distinctive megastructures that affected the early Tithonian to early Valanginian Vaca Muerta Formation, such as the Chihuidos High, the Huincul High, and the Agrio fold-and-thrust belt. Also, multiple fault systems forming kilometer-scale features were created. The main fault systems affecting the Vaca Muerta–Quintuco system are classified according to the Anderson classification: normal, reverse, and strike-slip faults. The following fault families are identified: five normal fault families (northwest–southeast, east-northeast–west-southwest, north-northeast–south-southwest, north-south, and radial), five reverse (high-angle) fault families (east–west, northeast–southwest, north–south, north-northeast–south-southwest, and circular), two thrust (low-angle) fault families (north-northwest–south-southeast and north-northeast–south-southwest), and one strike-slip fault family (east-northeast–west-southwest). The geometrical characteristics, orientations, and distribution of these Vaca Muerta fault families are presented and the interpretation of their genesis is discussed. Second-order structures such as volcanic dikes and sills, soft-sediment deformations and accomodation/transfer zones that participate to the deformation of the Vaca Muerta–Quintuco system are also described because they also affect the unconventional self-sourced play. Finally, some structural aspects of the Chihuidos High, the impact of the inheritance on the Vaca Muerta-Quintuco structures (geometry, orientation, and distribution) and the Structural Risk Analysis are discussed.