SHRIMP U-Pb zircon dating of Neoproterozoic granites from the easternmost São Roque Domain, Ribeira Belt

Abstract

Four granitic plutons from the easternmost portion of the São Roque Domain (SRD) were dated by U-Pb zircon SHRIMP; the results indicate that the peak of granitic magmatism was concentrated in a short interval (606-589 Ma), the same as in the central portion of the SRD. The two porphyritic biotite granites (Morro Azul and Imbiruçu) yield the oldest ages (respectively, 601.0 ± 4.9 Ma and 606.3 ± 4.8 Ma) and have inherited zircons with similar ages (-2.1-2.0 Ga), but are not comagmatic. The Morro Azul granite has geochemical signature similar to other high-K calc-alkaline (HKCA) granites from the SRD. while the Imbiruçu granite has much higher Sr/Zr and other chemical features that demand different sources. Other two dated samples are very different from each other and from the HKCA granites. The age of the Morro do Pão tonalite (589.1 ± 5.5 Ma) indicates that, in spite of its more deformed character, it is younger; a similar value, although with large uncertainty, is shown by the Serra dos índios peraluminous leucogranite (593 ±12 Ma). Our analytic data combined with field relationships suggest that soon after the mam episode of HKCA magmatism, the SRD witnessed the emplacement of granites of varied composition forming small bodies that recorded deformation associated with transcurrent tectonics.