A Provenance Analysis from the Lower Jurassic Units of the Neuquén Basin. Volcanic Arc or Intraplate Magmatic Input?

Abstract

A possible signal of the Jurassic Chon Aike Igneous Province within the early infill of the Neuquén Basin is recognized in our provenance analyses. We use a combination of detrital zircon geochronology and Lu–Hf isotope analysis, along with sandstone petrography descriptions to characterize the sediments source region in the Cuyo Group. The sandstone petrographic analysis confirms important contributions from volcanic sources of different compositions. U-Pb ages and Hf isotopes obtained in the analyzed zircons indicate a more complex configuration given by multiple igneous components. The variations in the provenance patterns allow us to make some observations about the paleogeographic evolution of the basin. At the base of the sequence, the sediments were derived from local sources composed of Permian basement and Upper Triassic volcanic rocks, whereas in the top, the zircons were supplied from Lower Jurassic volcanic rocks and Lower Paleozoic and Precambrian basements suggesting more distal and ancient sources. Low values of εHft (−15.5 to −0.7) analyzed in Permian and Triassic detrital zircons indicated an evolved source with strong crustal contribution. These data are in agreement with the negative values of εHft and εNdt calculated in Permian and Triassic igneous rocks from the North Patagonian Massif. The εHft about −4 of the Jurassic detrital zircons indicated a crustal origin for the source rocks and are clearly compatible with the isotopic compositions of the Chon Aike Igneous Province. A volcanic source region compatible with the Andean arc is dismissed because the Jurassic arc has isotope characteristics of a mantle source.