Constructional stages associated with the Malargue fold and thrust balt from thermochronological data and synorogenic strata

Abstract

Apatite fission-track analysis performed on eighteen Mesozoic sediment samples of the Neuquen Basin from the Southern Central Andes orogenic front between 35°30´ and 37°S has revealed Campanian-Paleoceno (75-55 Ma), late Eocene-early Oligocene (35-30 Ma) and middle Miocene (15-10 Ma) cooling episodes. Each cooling episode corresponds closely with major unconformities observed in the preserved sedimentary sequences, and is associated with kilometer-scale additional burial and subsequent exhumation. Asimilar degree of cooling is inferred from associated vitrinite reflectance data. Late Eocene-esrly Oligocene exhumation is recognized only near the eastern orogenic front adjacent to the foreland in the southernmost part of the study area and may be related partly to withinplate magmatism and associated extensin in the Palaoco Basion. The Campanian-Paleocene and middle Miocene cooling episodes are recognized more widely in the fold and thrust belt and appear to coincide with periods of eastward arc expansion and mountain building processes.