Evidence of multiple sources involved in the genesis of the neoproterozoic itapetim granitic complex, NE Brazil, based on geochemical and isotopic data

The Itapetim Complex is a multiple facies intrusion of porphyritic monzogranite hosting isolated, or swarms of, dioritic enclaves and cut by late dikes of biotite granodiorite. It is a syn-tectonic intrusion in relation to the D3 regional deformation phase of the Brasiliano Orogeny. The complex has contacts with metagreywackes and gneissic granites associated with the Mesoproterozoic Cariris Velhos event and, to the northwest, with a belt of gneisses of Paleoproterozoic ages. At least two different sources seem to be involved in the evolution of the Itapetim Complex. The diorite source appears to be a depleted mantle that underwent some small degree of mixture with a Paleoproterozoic enriched mafic crust. The monzogranite source is probably metagreywacke, a mixture of enriched crust of Paleoproterozoic age and volcanic rocks related to the Cariris Velhos event. The granodiorites were generated by partial melting of a source compositionally similar to those suggested for the monzogranite. U-Pb in zircon gave a crystallization age of 638 +/- 4.9 Ma for the porphyritic monzogranites and associated mafic rocks. The granodiorite dikes represent a late magmatic event, under intermediate fO(2) conditions. The dikes, intruded into brittle fractures, are probably related to 570 Ma intrusions within the Pajeu Paraiba Terrane. (C) 2000 Published by Elsevier Science Ltd.