Mesozoic tectonic inversion in the Neuquen Basin of west-central Argentina



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Texas A&M University


Mesozoic tectonic inversion in the Neuquen Basin of west-central Argentina produced two main fault systems: (1) deep faults that affected basement and syn-rift strata where preexisting faults were selectively reactivated during inversion based on their length and (2) shallow faults that affected post-rift and syn-inversion strata. Normal faults formed at high angle to the reactivated half-graben bounding fault as a result of hangingwall expansion and internal deformation as it accommodated to the shape of the curved footwall during oblique inversion. Contraction during inversion was initially accommodated by folding and internal deformation of syn-rift sedimentary wedges, followed by displacement along half-graben bounding faults. We suspect that late during inversion the weight of the overburden inhibited additional fault displacement and folding became the shortening-accommodating mechanism. A Middle Jurassic inversion event produced synchronous uplift of inversion structures across the central Neuquen Basin. Later inversion events (during Late Jurassic, Early Cretaceous, and Late Cretaceous time) produced an "inversion front" that advanced north of the Huincul Arch. Synchroneity of fault reactivation during the Callovian inversion event may be related to efficient stress transmission north of the Huincul Arch, probably due to easy reactivation of low-dip listric fault segments. This required little strain accumulation along "proximal" inversion structures before shortening was transferred to more distal structures. Later inversion events found harderto- reactivate fault segments, resulting in proximal structures undergoing significant inversion before transferring shortening. The time between the end of rifting and the different inversion events may have affected inversion. Lithosphere was probably thermally weakened at the onset of the initial Callovian inversion phase, allowing stress transmission over a large distance from the Huincul Arch and causing synchronous inversion across the basin. Later inversion affected a colder and more viscous lithosphere. Significant strain needed to accumulate along proximal inversion structures before shortening was transferred to more distal parts of the basin. Timing of inversion events along the central Neuquen Basin suggest a megaregional control by right-lateral displacement motion along the Gastre Fault Zone, an intracontinental megashear zone thought to have been active prior to and during the opening of the South Atlantic Ocean.