Siliciclastic Ordovician to Silurian units of the Argentine Precordillera: constraints on provenance and tectonic setting.

ABRE, PAULINA; CINGOLANI, CARLOS ALBERTO; CHEMALE JR., FARID; CAIRNCROSS, BRUCE

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2012 vol. 40 p. 1 - 22

0895-9811

Abstract A combination of petrography, geochemistry, Sm-Nd, Pb-Pb and U-Pb detrital zircon dating provide constraints to the provenance of Middle Ordovician to Early Silurian clastic sequences of the Precordillera s.s. as a part of the Cuyania terrane in western-central Argentina. The uniformity shown by the provenance proxies indicate that there were no important changes in the provenance within these units. A dominant upper crustal component is evident as well as a subordinate mafic input. Nd isotopes indicate åNd of -5.4, f Sm/Nd -0.34 and TDM 1.57 Ga in average for all the units studied. Pb-isotope ratios display average values for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb of 19.37, 15.86 and 39.43 respectively. Detrital zircon dating further constraints the input as being dominantly of Mesoproterozoic age (51-83%), but with contributions from NeoproterozoiceLower Cambrian (9-31%), Middle Cambrian to Ordovician grains (recorded up to 7%), and Palaeoproterozoic (2-7%) sources. The combination of the different provenance approaches applied indicates that the Mesoproterozoic Cuyania terrane basement, and partially the Pampia terrane were the main sources. The new information provided for the Ordovician to Silurian clastic sequences permitted enhanced the known geochemical and isotopic dataset to constrain the tectonic evolution of the Cuyania terrane. The interpretation of the obtained data supports that the terrane accretion to the proto-Andean margin of Gondwana probably occurred during Middle to early Upper Ordovician.