Mesozoic tectono-stratigraphic evolution of the Seychelles microcontinent

Abstract

The Seychelles region developed as a unique continental sliver through the three phases of rift tectonism that, since the Late Permian, created the western Indian Ocean. The history of rifting in Seychelles can perhaps be traced back to ∼ 700 Ma when the granites that form the central islands were emplaced. The low δ 18O of the high-temperature minerals within these slightly alkaline granites on Mahe indicate an intraplate origin, and the fracturing of the lithosphere consequent to their emplacement created a locus of weakness for future rift tectonism to exploit. Thermally induced extensional rifting, initiated during the Carboniferous and rekindled in the Late Permian (∼ 225 Ma), eventually severed Super-Gondwana in the Middle Jurassic (∼ 160 Ma) into East and West Gondwana. A proto-Indian Ocean, the Somali Basin which separated East and West Gondwana, ceased to expand in the Early Cretaceous (∼ 115 Ma). This rift/ drift event is recorded in Seychelles by block-faulted sequences of distal fluviatile, through near-shore to open marine deposits along its western margin and possibly at Farquhar. Within East Gondwana, transform rifting then separated Madagascar and Seychelles/ India in the Late Cretaceous. At 84 Ma a spreading ridge developed between these blocks forming the Mascarene Basin as a new arm of the evolving Indian Ocean. A thick progradational wedge of sediment, initially alluvial followed by lacustro-marine and eventually open marine, resulted from this event along the southwest Seychelles margin. Finally, hotspot-related thermally induced rifting, causing block-faulting and fluviatile to marine deposition, eventually separated Seychelles from India at the Cretaceous/ Tertiary boundary. This separation coincided with the Deccan volcanic event and the development of the Carlsberg Spreading Ridge, which replaced the Mascarene Spreading Ridge and initiated the opening of the northwestern Indian Ocean Basin. Sedimentation on the Seychelles microcontinent throughout the Tertiary produced predominantly shelf carbonates.