TUNIK Maisa Andrea
EARLY UPLIFT AND OROGENIC DEFORMATION IN THE NEUQUÉN BASIN: CONSTRAINTS ON THE ANDEAN UPLIFT FROM UPb AND Hf ISOTOPIC DATA OF DETRITAL ZIRCONS
TUNIK, MAISA ANDREA; FOLGUERA, ANDRES; NAIPAUER, MAXIMILIANO; PIMENTEL, MARCIO; RAMOS, VICTOR
ELSEVIER SCIENCE BV
Año: 2010 p. 257 - 273
Provenance of detrital sediments of the Neuquén Basin in Central Argentina wasinvestigated using U-Pb and Lu-Hf isotopic composition of zircon grains in order toevaluate 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 theNeuquén Group (Upper Cretaceous), as well as from older deposits of the Rayoso andAgrio Formations (Lower Cretaceous) were investigated. A regional angularunconformity separates the Upper from the Lower Cretaceous units and is generallyattributed to the onset of the foreland basin stage. The evident differences between thesesuites (above and below the unconformity) are clearly shown by their distinctprovenance 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 Famatinianorogen, the Lower Cambrian-Neoproterozoic Pampean orogen, the Grenvillian-ageMesoproterozoic basement and some other older sources. In contrast, detrital zirconsabove the unconformity, from the Candeleros Formation, have striking differentprominent peaks. The pattern indicates direct derivation from the Early Cretaceousmagmatic arc, probably from plutons uplifted during the Late Cretaceous deformation along the western Chilean slope of the Andean cordillera. The contrasting dispersalpatterns are interpreted as a result of the uplift of the southern Central Andes at theselatitudes. The youngest detrital zircons constrain the timing of uplift as being youngerthan 99 Ma, supporting the assumed Cenomanian age for the synorogenic deposits. Thisage is further constrained by fission-track data from zircons from an ash-tuff layer of thelowest parts of the Neuquén Group, which yielded ages of about 88 Ma. The Hf isotopicdata indicate derivation from a juvenile mantle for the Grenvillian age zircons, whichcorroborates the previously assumed island arc setting. The intermediate Hf isotopicvalues for the Pampean age zircons indicate a transition to the extensive recycling of thecontinental crust for the oldest Paleoproterozoic zircons with negative values thatcharacterize the foreland basement.