Géomorphologie evidence for Plio-Quaternary shortening in the southern Neuquén basin (40°S, Argentina).

A morphostructural analysi s of a Pliocene flood basalt forma-tion in the southern Neuquén basin (40°S) shows evidence of contractional deformation less than 3.5 Ma ago. This forma-tion exhibits a general dip towards the south-east, with relict outcrops located 100 m higher than the main source volcano, which suggests a local tilting of the lava flow. This tilt has been brought about by Plio-Quaternary reactivation of the eastern border of the Sanico Massif along two thrusts that offset the lava flow. Another long-wavelength bulge in the southern part of the lava flow unit indicates a possible Pliocene uplift of the North Patagonian Massif. These results provide new evidence of continuing shortening in the Neuquén basin during the Plio-Quaternary, challenging the hypothesis that an extensional regime has existed since the end of the Miocene in this basin. [ABSTRACT FROM AUTHOR]