Intraplate deformation in the Neuquén Embayment

Abstract

The Neuquén Embayment, which developed along the eastern foothills of thesouthern Central Andes, has a complex history of intraplate deformation. The Paleozoicbasement fabrics exerted a major influence in Mesozoic and Cenozoic deformation.The most important feature is an E-W–striking fault system that is related to alate Paleozoic fabric and is associated with the Huincul basement high, which truncatesthe basin. This fabric is interpreted as being the result of the accretion of thePatagonia terrane with Gondwana during the Early Permian. Two-dimensional (2D)and three-dimensional (3D) seismic coverage and subsurface information identify differentsectors in the Neuquén Embayment that record alternating episodes of contractionand extension during the Jurassic and Cretaceous. The deformation historyeast of the thrust front of the Agrio fold-and-thrust belt is characterized by periods of1) transpression and almost orthogonal contraction to the continental margin, (2)extension, and (3) relative quiescence, which alternates in different sectors. The earliestshortening occurred in the Early Jurassic when the main stress was oriented inthe N-NW sector. The stress rotated to the northwest up to Valanginian times, when amore orthogonal orientation to the continental margin became dominant and prevailedafter the Cenomanian. After a period of quiescence in the Neuquén Embaymentassociated with very oblique subduction during the Paleogene, the finalcontractional deformation took place in the late Miocene, with a west-east orientationof the main stress, and was followed by Pliocene extension.The changing stress patterns correlate with differences in convergence vectorsbetween the Aluk, Farallon, and Nazca oceanic plates and the Gondwana or SouthAmerican continental plates. The Aluk stage from the Jurassic to the Valanginian wascharacterized by tectonic inversion that is shown by shortening and right-lateralstrike-slip structures that are concentrated in the Huincul system and more subtledeformation in the Chihuidos and Entre Lomas systems. The early Farallon stage wasdistinguished by reduced inversion and displacement in the Huincul system and ageneral retreat of deformation after the Valanginian. The change to late Farallonstage was characterized by a prominent tectonic inversion of the Entre Lomas system,which resulted from the inception of the formation of the Agrio fold-and-thrustbelt in the retroarc area. This belt developed during most of the Late Cretaceous,when the embayment showed a general quiescence. The Nazca stage was characterizedby the main episode of uplift, tectonic inversion of the older half-grabens, andimportant strike-slip faulting that was followed by local collapse of some structuresduring the Pliocene.