U-Pb ages and Hf isotope compositions of zircons in plutonic rocks from the central Famatinian arc, Argentina

OTAMENDI, J.E.; DUCEA, M.; CRISTOFOLINI, E., ; ARMAS, P., CRISTOFOLINI, E., OTAMENDI, J., TIBALDI, A. Y BARZOLA, M.,; CAMILLETTI, G.; BERGANTZ, G.,

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2017

0895-9811

The Famatinian arcformed around the South Iapetus rim during the Ordovician, when oceaniclithosphere subducted beneath the West Gondwana margin. We present combined insitu U?Th?Pb and Lu?Hf isotope analyses for zircon to gain insights into the originand evolution of Famatinian magmatism. Zircon crystals sampled from fourintermediate and silicic plutonic rocks confirm previous observations showingthat voluminous magmatism took place during a relatively short pulse betweenthe Early and Middle Ordovician (472 ? 465 Ma). The entire zircon populationfor the four plutonic rocks yields coherent εHf negative values and spreadsover several ranges of initial εHf(t) units (-0.3 ? -8.0). The rangeof εHf units in detrital zircons of Famatinian metasedimentary rocks reflects aprolonged history of the cratonic sources during the Proterozoic to theearliest Phanerozoic. Typical tonalites and granodiorites that contain zirconswith evolved Hf isotopic compositions formed upon incorporating(meta)sedimentary materials into calc?alkaline metaluminous magmas. The evolvedHf isotope ratios of zircons in the subduction related plutonic rocks stronglyreflect the Hf isotopic character of the metasedimentary contaminant, eventhough the linked differentiation and growth of the Famatinian arc crust wasdriven by ascending and evolving mantle magmas. Geochronology and Hf isotopesystematics in plutonic zircons allow us understanding the petrogenesis ofigneous series and the provenance of magma sources. However, these data couldbe inadequate for computing model ages and supporting models of crustal evolution.