SHRIMP U/Pb zircon geochronology of Neoproterozoic juvenile and crustal-reworked terranes in southernmost Brazil

J.A.M. Leite, L.A. Hartmann, Neal Mcnaughton, F. Chemale

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    U/Ph zircon ages of sire rock units fi om southernmost Brazil were obtained by means of SHRIMP II techniques. The studied rocks occur on either side of the Neoproterozoic contact between a juvenile accreted terrace (the Vila Nova Terrane) and a crustal-reworked belt (the Dom Feliciano Belt). This contact is located in the western portion of the exposed Precambrian rocks in the state of Rio Grande tio Sul. Brazil.Contrasting patterns of U/Ph ages are shown by zircons hosted in metamorphosed basic and granitic rocks of the Cerro Mantiqueiras region and in the post-tectonic Lavras Granite, both located in the Vila Nova Terrane and in the syntectonic crust-derived Cacapava Granite in the Dom Feliciano Belt. Contrasting isotopic characteristics also are supported by Nd and Sr isotopes. For the Vila Nova Terrane, Nd model ages are no older than 1.3 Ca, epsilon Nd(740 Ma) values are between +2 and +6 and Sr-87/Sr-86 ratios are low, similar to 0.704 (Babinski et al., 1995; Leite. 1997). In the Dom Feliciano Belt, in contrast. Nd model ages are older, close to 2.2 Ga: epsilon Nd(620 Ma) values are strongly negative, at similar to-15, and Sr-87/Sr-86 ratios are higher than 0.710 (Babinski et al., 1996).SHRIMP U/Pb zircon data from the Cerro Mantiqueiras region indicate the occurrence of two main tectonometamorphic events during the development of the Brazilian/Panafrican orogenic cycle-the Sao Gabriel event at similar to 750 Ma and the Dom Feliciano event at similar to 580 Ma. The possible existence of a third. older event is suggested by an 890 Ma age for the Passinho Metadiorite. In marked contrast. U/Ph zircon data for the Cacapava Granite, in the Dom Feliciano Belt, range from nearly 2.4 Ga to 550 Ma: the older ages are interpreted as inheritance from an older crust, whereas the younger ones represent the magmatic age of the Cacapava Granite, corresponding to the late stages of the Dom Feliciano event. This event is represented in the Cerro Mantiqueiras region by the intrusion of the post-tectonic Lavras Granite, with a magmatic age of 580 Ma.
    Original languageEnglish
    Pages (from-to)688-705
    JournalInternational Geology Review
    Publication statusPublished - 1998

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