Miocene to Quaternary deformation of the Guañacos fold-and-thrust belt in the Neuquén Andes between 37°S and 37°30′S

Abstract

The fold and thrust belt of the Neuquén Andes between 37° and 37°30´S can be divided into two sectors that show contrasting evolutionary styles.The outer or eastern section contains the relatively well known Agrio and Chos Malal fold and thrust belts which were active from the Late Cretaceous to the late Miocene.The inner or western sector contains the Guañacos fold and thrust belt that is the subject of this paper. In contrast to the outer sector belts, contractional deformation in the Guañacos fold and thrust belt started during the late Miocene and continues today.The Guañacos belt is particularly noteworthy for being out-of-sequence in that the youngest deformation occurs in the inner sector of the deformational belt in the Pleistocene volcanic arc, in contrast to the usual situation in the where the youngest brittle deformation occurs in the outer sector.In detail, the Guañacos belt is located proximal to the present volcanic arc and coincides with the maximum heights of the Neuquén Andes.This thrust belt formed in response to tectonic inversion of an Oligocene-Miocene intra-arc rift.Detailed structural traverses in three valleys and observations in two other through this 60 km wide thrust belt show that the youngest tectonic activity is concentrated in the easternmost 40 km.Over the last 5 m.y., folds and thrusts in the Guañacos belt have affected Pliocene to lower Pleistocene volcanic arc rocks as well as Quaternary deposits that occur immediately east of the upper Pleistocene to Holocene centers of the Southern Volcanic Zone. Among the volcanic rocks incorporated into the Guañacos fold and thrust belt are those of the Pliocene to Quaternary Trohunco caldera and the Los Cardos-Centinela volcanic center.