Maximiliano Naipauer

U–Pb detrital zircon ages of Upper Jurassic continental successions: implications for the provenance and absolute age of the Jurassic–Cretaceous boundary in the Neuquén Basin

Abstract New U–Pb detrital zircon ages are presented for the Tordillo Formation. The ages indicate that the most important source region of sediment supply was the Jurassic Andean arc (peaks at c. 144, 153 and 178 Ma), although two secondary sources were defined at c. 218 and 275 Ma. Temporal variation in the provenance indicates that at the beginning of the sedimentation, Carboniferous to Lower Jurassic magmatic rocks and Lower Palaeozoic metamorphic rocks were the most important sources. Towards the top, the data suggest that the Andean arc becomes the main source region. The comparison between provenance patterns of the Tordillo Formation and of the Avilé Member (Agrio Formation) showed some differences. In the former, the arc region played a considerable role as a source region, but this is not identified in the latter. The results permit a statistically robust estimation of the maximum deposition age for the Tordillo Formation at c. 144 Ma. This younger age represents a discrepancy of at least 7 Ma from the absolute age of the Kimmeridgian and Tithonian boundary (from the chronostratigraphic timescale accepted by the International Commission of Stratigraphy, IUGS), and has strong implications for the absolute age of the Jurassic–Cretaceous boundary. Supplementary material: Sample coordinates, values of the sandstone compositional framework and U–Pb (LAM-MC-ICP-MS) age measurements of zircons grains are available at http://www.geolsoc.org.uk/SUP18718

Changes in Source Areas at Neuquén Basin: Mesozoic Evolution and Tectonic Setting Based on U–Pb Ages on Zircons

The Neuquen Basin constitutes a key site to investigate how the pattern of detrital zircon age varies through time in different tectonic regimes. Here we analyze the U–Pb zircon age database published for the Southern Central Andes. In the early Mesozoic (rift stage) the source regions were locally and strongly influenced by the active volcanism coeval with the extensional tectonic activity. The rift relief associated with the synrift stage lasted until the first marine transgression corresponding to the Los Molles Formation. The source regions in the retroarc setting (sag stage) are variable and showed reversal provenance. In the Middle and Late Jurassic the magmatic arc became the most important source, but in the Early Cretaceous eastern cratonic regions were the main source areas of sediment contribution. The reversal of the provenance pattern can be either explained by the base-level fall or by a period of exhumation of the Sierras Pampeanas basement linked to generation of rift systems. The source regions in the Late Cretaceous (foreland stage) indicate an uplift of a mountain chain and exhumation along the Andean magmatic arc; although younger and distal units showed that a peripheral bulge would be growing in the eastern cratonic sector. Cawood’s tectonic discrimination diagram is tested as a useful tool in the Southern Central Andes. However, it is necessary to consider more complex settings taking into account the relative positions of the magmatic arc and the orogenic front through time.

Growth of the Southern Andes

GOCE satellite data and EGM2008 model are used to calculate the gravity anomaly and the vertical gravity gradient, both corrected by the topographic effect, in order to delineate main tectonic features related to density variations. In particular, using the Bouguer anomaly from GOCE, we calculated the crust–mantle discontinuity obtaining elastic thicknesses in the frame of the isostatic lithospheric flexure model applying the convolution method approach. Results show substantial variations in the density, compositional and thermal structure, and isostatic and flexural behavior of the continental lithosphere along the Southern Andes and adjacent foreland region.

An Introduction to the Southern Andes (33–50°S): Book Structure

This book intends to constitute a useful tool to access to data and a general discussion about the mechanisms that have been associated with the development of the Southern Andes. It is mainly conceived for Earth Science professionals working in academia and industry, as well as Ph.D and Ms students and interested readers in general.

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

A possible signal of the Jurassic Chon Aike Igneous Province within the early infill of the Neuquen 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 eHft (−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 eHft and eNdt calculated in Permian and Triassic igneous rocks from the North Patagonian Massif. The eHft 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.