Late Cretaceous synorogenic deposits of the Neuquén Base (36-39◦): Age contrains from U-Pb dating in detrital zircons.

RAMOS, V. A.; PIMENTEL, M.; TUNIK, MAISA ANDREA

Niza

Congreso; 7th International Symposium on Andean Geodynamics; 2008

The inception of orogenic uplift in the Neuquén Basin was subject of intense debate in the last decades. Some authors favour the initiation of the orogenic shortening and development of the foreland basin stage in the latest Cretaceous associated with the deposition of the Malargüe Group during Maastrichtian-Paleocene times, with the major orogenic uplift during the Miocene time. alysis has been made.The age patterns of the detrital zircons analyzed by ICPMS show contrasting features indicating different sources in their provenances. One population is very similar to the standard pattern of the Early Cretaceous deposits, where the detrital zircons are mainly derived from the foreland region and therefore matching the age distribution of the basement provinces. In these sequences only some isolated and rare tuffs are derived from the magmatic arc. On the other hand, the detrital zircons from the synorogenic deposits have a conspicuous pattern of Early Cretaceous ages associated with a minor frequency of Jurassic age. Both Early Cretaceous and Jurassic ages indicate that the main arc has been uplifted and it was under erosion at the time of deposition of the Neuquén Group. The youngest ages of the Neuquén Group between 98 and 100 Ma constrain the maximum age of deposition to the base of the Cenomanian as it has been postulated by its fossil content. Once more the detrital zircons from sedimentary rocks are contributing to date fossils of poor stratigraphic value.