Geologia USP. Série Científica (Aug 2003)

U-Pb (Zircon) Ages of Metavolcanic Rocks From the Itaiacoca Group: Tectonic Implications

  • Oswaldo Siga Jr.,
  • Miguel Angelo Stipp Basei,
  • Kei Sato,
  • Hélcio José dos Prazeres Filho,
  • Leonardo Fadel Cury,
  • Werner Weber,
  • Cláudia Regina Passarelli,
  • Ossama Mohamed Harara,
  • José Manoel dos Reis Neto

Journal volume & issue
Vol. 3
pp. 39 – 49

Abstract

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The main aim of this work is to present and discuss the U-Pb ages obtained for zircon grains from metavolcanic rocks of theItaiacoca Group. The Itaiacoca Group is a metavolcano-sedimentary sequence, which occurs as a narrow belt between theCunhaporanga granitic batholith to the northwest and the Itapirapuã shear zone to the south and southwest, which separates thesequence from the Três Córregos granite batholith and metasedimentary rocks of the Açungui Group. Geological studies of thesouthern part of the Itaiacoca belt led to the recognition of three units, represented (from base to top) by metawackes with animportant volcanic component, metacarbonate, and metapelitic and metapsammitic rocks. The U-Pb geochronological analyses ofzircon grains from two outcrops of metavolcanic rocks yield ages of 628 ± 18 Ma (SHRIMP) and 636 ± 30 Ma (conventional multigrainanalyses). These ages are quite close to the metamorphic event recorded in the Itaiacoca Group (628 – 610 Ma), suggesting ashort interval between the formation of these rocks and closure of the basin. Furthermore, this volcanism is very close to the age offormation of the Três Córregos (630 Ma) and Cunhaporanga (590 Ma) granitic batholiths, admitted as associated with a probablemagmatic arc. Such an isotopic pattern characterizes a Neoproterozoic tectonic scenario involving volcanism, metamorphism andgranitic plutonism, interpreted here as the final stages in the evolution of the Itaiacoca Basin.

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