U-Pb geochronology of Seychelles granitoids: a Neoproterozoic continental arc fragment

New high-precision U-Pb zircon ages for 14 granitoid rocks of the Seychelle s, including samples from Mahe, Praslin, La Digue, Ste. Anne, Marianne, Fre gate and Recifs Islands, yield dates between 748.4 +/- 1.2 Ma and 808.8 +/- 1.9 Ma, interpreted as representing magmatic crystallization ages. U-Pb zi rcon ages as young as 703 Ma have been reported by other workers, and the t ime span of Seychelles magmatic activity, therefore, is similar to 100 Myr. The vast majority of ages, however, fall in the period 748-755 Ma, suggest ing a major period of granite plutonism at this time. At least some Seychel les dolerite dikes have equivalent ages, indicating the contemporaneity of granitic and basaltic magmas, and supporting field and chemical evidence fo r the production of minor quartz dioritic rocks by hybridization and magma mingling. Possible correlatives of the late Neoproterozoic (similar to 700- 800 Ma) granitoids and dolerites of the Seychelles include volcanic and plu tonic rocks in Madagascar and northwestern India (Malani Igneous Suite, Raj asthan), which may have formed in a continuous continental (Andean-type) ar e located at the western margin of the Rodinia supercontinent. This idea is more consistent with the time span of magmatism, petrologic character of t he igneous rocks, and paleomagnetically determined reconstructions, than th e commonly held view of an intra-plate extensional setting for the Seychell es and Malani Igneous Suite. (C) 2001 Elsevier Science B.V. All rights rese rved.