Structure of the Seychelles archipelago
Installing a landstation on Mahe
The granitic islands of the Seychelles Plateau have long been recognised to overlie continental crust, isolated from Madagascar and India during the formation of the Indian Ocean. However, to-date the extent of continental crust beneath the Seychelles region remains unknown. This is particularly true beneath the Mascarene Basin between the Seychelles Plateau and Madagascar and beneath the Amirante Arc. Constraining the size and shape of the Seychelles continental fragment is needed for accurate plate reconstructions of the breakup of Gondwana and has implications for the processes of continental breakup in general.
To help solve this problem we installed a network of broadband seismometers throughout the Seychelles archipelago for a period of a year. We then estimated crustal thickness and Vp/Vs from H-k stacking of receiver functions. The results were verified by forward modelling ship-collected gravity data. The majority of the Seychelles Islands away from the topographic plateau show no direct evidence for continental crust. The exception to this is the island of Desroche on the northern Amirante Ridge, where thicker low density crust, consistent with a block of continental material is present. We suggest that the northern Amirantes are likely continental in nature and that small fragments of continental material are a common feature of plume affected continental breakup.
Cartoon showing the formation of the Indian Ocean. At ~90 Ma (left) the eruption of the Marion plume initiates rifting between Greater India (India, Seychelles, Mauritia and other fragments) and Madagascar. Following the eruption of the Deccan plume that initiated rifting between India and the Seychelles, the Indian Ocean was left with a series of isolated micro-continents (right). A=Amirante Ridge, LR=Laxmi Ridge, M=Madagascar, S=Seychelles.
Hammond, J. O. S., 2007. Imaging the upper- mantle beneath the Seychelles: Architecture of a microcontinent, University of Leeds.
Hammond JOS, Kendall J-M, Collier JS, Helffrich G, Rumpker G, (2013). The extent of continental crust beneath the Seychelles, Earth and Planetary Science Letters, Vol:381, Pages:166-179 (doi)
Hammond JOS, Collier JS, Kendall J-M, Helffrich G, Rumpker G, (2012). Plume scar in the mantle lithosphere beneath the Seychelles revealed by seismic imaging, Earth and Planetary Science Letters, Vol:381, Pages:166-179 (doi)