Reactivation of Cretaceous structures during the Miocene deformation, Agrio fold and thrust belt, Neuquén.

Abstract

The most recent studies in this area of the Andes of Neuquén have shown the existence of an important deformational event at the end of the early Cretaceous and a later reactivation during the Miocene. Recent Ar-Ar ages have constrained the first event and Miocene synorogenic deposits the second. New evidence from paleomagnetic data and structural information that corroborate both events are presented in this paper. The paleomagnetic data are from Paleocene-Eocene sills of the Collipilli group. They show that these sills were intruded in a deformed sedimentary sequence dipping about 25º and later rotated to their current position. In addition, the analysis of the discordance between the Tralalhué synorogenic conglomerate and the Agrio and Rayoso Formations has verified a 20º angular unconformity at the time of the deposition of the synorogenic deposits. Putting this evidence together demonstrates that the Cretaceous deformation tilted the sedimentary sequence 20-25º and later, in the Miocene, these structures were reactivated.