Abstract
The rocks of Sierra de Maz and Sierra del Espinal (Western Sierras Pampeanas) represent pre-Famatinian (Ordovician) basement. Isotope compositions (Nd and Pb) of metasedimentary rocks and SHRIMP U–Pb dating of detrital zircons, combined with other geological evidence, show that three parallel N–S domains can be recognized. The central Maz Domain contains pre-Grenvillian metasedimentary rocks deposited between 1.2 and 1.6 Ga, that underwent Grenvillian granulite facies metamorphism and were intruded by mafic igneous rocks and massif-type anorthosites. Metasedimentary rocks have high Nd T DM ages (1.7–2.7 Ga) and very radiogenic Pb ( μ = 9.8–10.2), suggesting provenance from reworked early Proterozoic or Archean continental crust. The domains to the east and west of the Maz Domain consist of three metasedimentary sequences with Nd T DM ages between 1.2 and 1.6 Ga and variably radiogenic Pb ( μ = 9.6–10.0). U–Pb SHRIMP dating of detrital zircons, Nd T DM model ages and comparison with other data suggest that these sequences are post-Grenvillian, i.e., Neoproterozoic and/or early Paleozoic. The Maz Domain is interpreted as a suspect terrane similar to the northern Arequipa–Antofalla craton that forms the basement of the Central Andes; both underwent Grenville-age orogeny and were probably once continuous along the western margin of Amazonia (West Gondwana).
Highlights
The Western Sierras and the basement of the central Andes (Fig. 1) constitute two exposures of pre-Andean rocks where tectonothermalGrenville age
We provide here new Nd and Pb isotope compositions and U Pb SHRIMP zircon data from the Western Sierras Pampeanas (Sierra de Maz, Sierra del Espinal and adjoining sierras)
U-Pb zircon evidence of Famatinian-rejuvenated Protero zoic terranes of Grenvillian age (1.0 to 1.2 Ga) in the Western Sierras Pampeanas was first found in the Sierra de Pie de Palo (1vIcDonough et aI., 1993; Casquet et aI., 2001; Vujovich et aI., 2004)
Summary
The Western Sierras and the basement of the central Andes (Fig. 1) constitute two exposures of pre-Andean rocks where tectonothermal. Grenville belt all four continental masses and extends into the mobile belts in Australia (Wingate et aI., 1998; et aI., 2003) To date these models do not take account of the Western Sierras t'atnp,earlas. We provide here new Nd and Pb isotope compositions and U Pb SHRIMP zircon data from the Western Sierras Pampeanas (Sierra de Maz, Sierra del Espinal and adjoining sierras) These data suggest the outline of a new terrane of Mesoproterozoic age that underwent Grenville-age orogeny. This terrane shows isotopic and geological similarities with the central and northern part of the Arequipa-Antofalla craton of Pem and nor thern Chile, and Amazonia, suggesting that they were probably all once part of a continuous belt of Grenvillian reworked basement largely autochthonous to Amazonia (Western Gondwana). The Maz suspect terrane is tectonically imbricated with post-Gren villian terranes, probably as a consequence of the Famatinian (i.e. Ordovician) orogeny and younger faulting
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