Tracing crustal evolution in the southern central Andes from Late Precambrian to Permian with geochemical and Nd and Pb isotope data

Major and trace element abundances and Nd and Pb isotopes of sedimentary an d igneous rocks of Late Proterozoic to Permian age from northwest Argentina and northern Chile (northern Puna) have been analyzed to evaluate paleogeo graphic reconstructions and the crustal evolution of the Pacific margin of Gondwana during the Paleozoic. Recycling of material solely derived from pr eexisting material of western Gondwana can explain the isotope compositions of the sedimentary samples. Major and trace element compositions of the se dimentary samples are similar to upper continental crust and show no system atic changes during the Paleozoic. Pre-Ordovician and Ordovician sedimentar y samples of the eastern belt of the northern Puna have homogeneous crustal epsilon(Nd) (450 Ma) values of -7.0 +/- 1.0 (T-DM = 1.6 to 1.8 Ga). A rang e of about six epsilon-units (epsilon(Nd) [450 Ma] = -7.8 to -1.3) is obser ved within the Arenigian Volcanosedimentary Successions, indicating the app earance of a short-lived juvenile source. All samples of the overlying Puna Turbidite Complex show a narrow range of crustal epsilon(Nd) (450 Ma) valu es (-7.0 +/- 0.3). Late Paleozoic sedimentary samples from northern Chile ( epsilon(Nd) [450 Ma] = -7 to -4) are comparable to the Ordovician values an d may be derived from local sources such as the Ordovician granitoids of th e Cordon de Lila Complex (epsilon(Nd) [450 Ma] -4.8 to -5.4) or by recyclin g of the Volcanosedimentary Successions. They require no exotic source. Pb isotope data support the homogeneous makeup of the margin indicated by the Nd isotopes. We did not find evidence for juvenile are magmatism or obducti on of ocean floor.