HR: 11:30h
AN: U52A-05    [Abstracts]
TI: Compression vs. Extension in the Central Neuquen Basin (35°-37°S), Argentina
AU: * Dhont, D
EM: damien.dhont@univ-pau.fr
AF: University of Pau et des Pays de l'Adour, CNRS-UMR 5212 : Modeling and Imagery in Geosciences IPRA Avenue de l'Universite, Pau, 64000, France
AU: Backe, G
EM: guillaume.backe@adelaide.edu.au
AF: The University of Adelaide, Geology and Geophysics School of Environment and Earth Sciences DP 313, Adelaide, 5005, Australia
AU: Hervouet, Y
EM: yves.hervouet@univ-pau.fr
AF: University of Pau et des Pays de l'Adour, CNRS-UMR 5212 : Modeling and Imagery in Geosciences IPRA Avenue de l'Universite, Pau, 64000, France
AB: The present day geometry of the Neuquen basin located in the southernmost part of the Central Andes is inherited from different compressive pulses during the Late Cretaceous-Late Miocene time interval. However, the structural evolution of the central Neuquen basin (35°-37°S) during the Late Cenozoic is still a matter of debate. Some authors argue for compression since the Late Miocene onwards whereas others favor extension during the Quaternary. Here we present evidences of compressive, extensive and strike-slip structures of Quaternary age. Several observations show that thrusting and folding is still active during the Quaternary in the external part of the Neuquen basin: alluvial fans are deformed and Quaternary alluviums are uplifted respectively in the footwall and the hanging wall of the Tromen thrust; Quaternary terraces are folded with progressive unconformities along the external limb of the Pampa de Tril anticline; regressive erosion develops in the eastern part of the basin along the east limb of the Chihuidos anticline. We have also documented numerous normal faults of various ages. Syn- sedimentary normal faults developed during the Late Jurassic-Early Cretaceous close and parallel to the eastern border of the Loncopue through (western part of the Neuquen basin). The Mesozoic sediments are cut by some N160°E-trending hydrothermally altered normal faults that may have initiated in association with volcanism. This latter ~E-W extension may be contemporary with the formation of the Loncopue through during the Oligocene. In the central part of the Neuquen basin, we have observed normal faults affecting Quaternary terraces. Along the east limb of the Tromen volcano, normal faults postdate the Tromen thrust. In the northeastern part of the study area, a major N-S right-lateral strike-slip fault affects the Holocene lavas of the Payun volcano. The coexistence of both recent compressive and extensive tectonic structures seems to be contradictory at the scale of the Neuquen basin. However, this apparent contradiction may be explained by the development of relay zones at the stepovers of strike-slip faults trending N-S. A strike-slip tectonic regime characterized by a maximum horizontal principal stress axis trending NE-SW agrees well with the initiation of recent normal faults striking in the same direction. We propose that the central Neuquen basin corresponds to a particular area forming an extensional relay zone between (1) to the southwest, the N-S Liquine-Ofqui right-lateral strike fault that vanishes at the latitude of the study area and (2) to the northeast, a N-S right-lateral strike-slip fault cutting the Holocene lavas. Compression may also develop locally at stepovers along strike-slip fault segments. The central Neuquen basin is therefore controlled by strain partitioning in the frame of the oblique convergence between the Nazca and the South America plates.
DE: 8104 Continental margins: convergent
SC: Union [U]
MN: 2007 Joint Assembly