Oldest age of magmatism in the Passinho arc in the ...
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Oldest age of magmatism in the Passinho arc in the ...
Gondwana during the Tonian and Cryogenian. Key words: São Gabriel terrane, LA-(MC) ICP-MS, U-Pb isotopes,. Neoproterozoic, Zircon geochronology.
Oldest age of magmatism in the Passinho arc in the southwestern portion of Gondwana, Rio Grande do Sul, Brazil. Ruy Paulo Philipp1, Marcelo Lusa2, Miguel A.S. Basei3; Léo Afraneo Hartmann1, João Orestes S. dos Santos4 The Passinho arc constitutes the south portion of the São Gabriel terrane, a major tectonic component of the Dom Feliciano belt along the Rio de La Plata craton. The arc formed as result of the convergence of the Amazonian and Rio de La Plata cratons between 900 and 680 Ma. The arc is preserved in those region situated south of the Cerro da Mantiqueira ophiolite. New in situ zircon U-Pb isotope data by LA-MC-ICP-MS on representative ortogneisses from the Imbicui Gnaisses (Cambai Complex) led the characterization of the oldest Neoproterozoic magmatic event in the São Gabriel terrane. Zircons from a tonalitic gneiss yielded U-Pb crystallization age of 875±5 Ma; few inherited zircons display Paleoproterozoic U-Pb ages of 2124±14 Ma and 2121±13 Ma, suggesting a contribution of ancient crust in the petrogenesis of the host magmas. The gneisses have a low-K calc-alkaline composition suggesting that the host magma derived from a depleted mantle. The gneisses are cut by diorites of the Santa Siria Diorite that presents a concordia age of 744.5±1.2 Ma. The rocks of the São Gabriel arc have younger zircons, with U-Pb SHRIMP ages of 735 to 710 Ma for the ortogneisses of the Vila Nova region and in the 730 to 740 Ma for the granitoids of the Lavras do Sul region. These ages suggest the existence of two magmatic arcs in the southwestern border of Gondwana during the Tonian and Cryogenian.
Key words: São Gabriel terrane, LA-(MC) ICP-MS, U-Pb isotopes, Neoproterozoic, Zircon geochronology.
