EARLY UPLIFT AND OROGENIC DEFORMATION IN THE NEUQUÉN BASIN: CONSTRAINTS ON THE ANDEAN UPLIFT FROM U–Pb AND Hf ISOTOPIC DATA OF DETRITAL ZIRCONS

MAISA TUNIK, ANDRÉS FOLGUERA, MAXIMILIANO NAIPAUER, MARCIO PIMENTEL AND VICTOR A. RAMOS

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Año: 2010 p. 1 - 48

0040-1951

Provenance of detrital sediments of the Neuquén Basin in Central Argentina was investigated using U-Pb and Lu-Hf isotopic composition of zircon grains in order to evaluate the timing of uplift of the southern Andes at these latitudes (36°-39°S). Samples of fluvial synorogenic deposits of the Candeleros Formation, at the base of the Neuquén Group (Upper Cretaceous), as well as from older deposits of the Rayoso and Agrio Formations (Lower Cretaceous) were investigated. A regional angular unconformity separates the Upper from the Lower Cretaceous units and is generally attributed to the onset of the foreland basin stage. The evident differences between these suites (above and below the unconformity) are clearly shown by their distinct provenance patterns, which correspond to different bedrock sources and patterns ofdispersal. Detrital zircons of the Rayoso and Agrio Formations beneath theunconformity indicate provenance from the eastern foreland basement, presentlyexposed along the Sierras Pampeanas of central Argentina. Detrital-zircon agescorrespond to the Permian and Triassic Choiyoi province, the Ordovician Famatinian orogen, the Lower Cambrian-Neoproterozoic Pampean orogen, the Grenvillian-age Mesoproterozoic basement and some other older sources. In contrast, detrital zircons above the unconformity, from the Candeleros Formation, have striking different prominent peaks. The pattern indicates direct derivation from the Early Cretaceous magmatic arc, probably from plutons uplifted during the Late Cretaceous deformation.