Evidence of Middle Jurassic magmatism within the Seychelles microcontinent: Implications for the breakup of Gondwana

The breakup of East and West Gondwana occurred during the Jurassic, but the exact timing is uncertain due to the limited exposure of rocks suitable for radioisotopic dating. Trachytic rocks from Silhouette Island, Seychelles, yielded a range of zircon ages from Paleoproterozoic to Cenozoic. The Pb-206/U-238 age of the trachyte is 64.9 +/- 1.6 Ma (Danian) but the majority of zircons yielded an age of 163.8 +/- 1.8 Ma (Callovian) with a small subset yielding an age of 147.7 +/- 4.5 Ma (Tithonian). The Hf isotopes of the Callovian (epsilon(Hf)(t) = +4.1 to +13.4) and Danian (epsilon(Hf)(t) = +1.9 to +7.1) zircons indicate that they were derived from moderately depleted mantle sources whereas the Tithonian zircons (epsilon(Hf)(t) = -7.0 to -7.3) were derived from an enriched source. The identification of middle Jurassic zircons indicates that rifting and magmatism were likely contemporaneous during the initial separation of East and West Gondwana.