ID-TIMS using the step-wise dissolution technique versus ion microprobe U–Pb dating of metamict Archean zircons from NE Madagascar

A geochronological study using the step-wise dissolution technique and in situ ion microprobe analysis is applied to late Archean metamict zircons of granitoids from northeastern Madagascar basement. Both techniques provide concordant U–Pb ages. Additionally, the ion microprobe study provided in situ measurements on the Pb isotopic composition of the metamict domains. Finally, Pb–Pb evaporation ages were found to be slightly but systematically younger than the dating obtained by the two other methods. Based on these data, granites from the Antongil belt were emplaced during at least three episodes separated by periods of magmatic inactivity of about 10 Ma at 2513, 2523 and 2532 Ma, respectively. These results are consistent with previous whole-rock Rb–Sr and U–Pb zircon dating from this part of Madagascar. The occurrence of this late Archean basement in northeastern Madagascar can be related to southern India where large volumes of contemporaneous granitoids were emplaced.