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U-Pb zircon geochronology of Precambrian tin-bearing continental-type acid magmatism in central Brazil

1991; Elsevier BV; Volume: 52; Issue: 3-4 Linguagem: Inglês

10.1016/0301-9268(91)90086-p

1872-7433

Márcio Martins Pimentel, Larry M. Heaman, Reinhardt A. Fuck, Onildo João Marini,

Paleontology and Stratigraphy of Fossils

U-Pb geochronological data for alkali-rich granitic and associated rhyolitic rocks from two different tin-bearing sub-provinces of the Goiás tin province, in central Brazil, reveal two distinct episodes of mid-Proterozoic continental acid magmatism at ca. 1770 Ma and 1600 Ma ago. U-Pb zircon data for the Sucuri and Soledade granites of the eastern Rio Paranà Sub-Province (RPS) define upper intercept ages of 1767±10 Ma and 1769±2 Ma, respectively. These ages are indistinguishable from a U-Pb age of a rhyolite from the basal portion of the Araí Group (1771±2 Ma). These results attest to the contemporaneity of the intrusion of the granites and the crystallization of the rhyolitic lavas in the Rio Paranà Sub-Province. U-Pb isotopic results from zircons from the Serra da Mesa granite in the western Rio Tocantins Sub-Province (RTS) indicate that the granitic igneous activity in that area is ca. 150 Ma younger than that in the RPS. The inheritance pattern observed in the zircons from the Araí rhyolite suggests that the sialic basement in the RPS region may include an early Proterozoic (ca. 2.2 Ga) component. Inheritance of possibly Archaean age was also found in zircons from the Sucuri granite. Lower intercept age of 658 Ma for the Soledade granite zircons indicate Pb loss during the late Proterozoic Brasiliano (Pan-African) thermo-tectonic event (650-550 Ma). Similar associations of tin-bearing, alkali-rich granites with rhyolites and succeeding continental sediments are known in other parts of the Precambrian shield of Brazil. This indicates that extensive areas of this shield experienced extensional tectonics in intracontinental settings between ca. 1700 and 1900 Ma ago.