HR: 1340h
AN: T13A-0450    [Abstracts]
TI: Crustal Structure and Evidence for a Hales Discontinuity Beneath the Seychelles Microcontinent
AU: * Hammond, J
EM: j.hammond@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Leeds, Ls2 9JT United Kingdom
AU: Kendall, J
EM: gljmk@bristol.ac.uk
AF: University of Bristol, Department of Earth Sciences, Bristol, BS8 1RJ United Kingdom
AU: Collier, J
EM: jenny.collier@imperial.ac.uk
AF: Imperial College London, Department of Earth Science and Engineering, London, SW7 2AZ United Kingdom
AU: Rumpker, G
EM: rumpker@geophysik.uni-frankfurt.de
AF: Johann Wolfgang Goethe-Universit„t Johann Wolfgang Goethe-Universit„t, Arbeitsbereich Geophysik, Frankfurt, D-60323 United Kingdom
AU: Pilidou, S
EM: s.pilidou@yahoo.co.uk
AF: University of Leeds, School of Earth and Environment, Leeds, Ls2 9JT United Kingdom
AU: Stuart, G
EM: g.stuart@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Leeds, Ls2 9JT United Kingdom
AB: It is well known that the Seychelles Plateau consists of a sliver of continental crust cast adrift during the formation of the Indian ocean. However the extent of the continental crust beneath the microcontinent and the cause of its isolation is poorly understood. Here we use receiver functions, interstation phase velocities obtained from surface waves, and wide angle reflections from controlled-source seismic data to investigate the lithospheric structure of the region. The H-κ method is used to calculate depths and Poison's ratio at 26 temporary stations distributed across the plateau and Mascarene basin. The V_p/V_s ratios and depths at stations on the plateau are typical of continental crust. To explain the major features of the RFs a simple two layer crust is proposed for the island of Mahé. The islands of Silhouette and Nord display a more complex crust consistent with the islands volcanic history. Praslin and its satellite islands display a simpler crust but display signs of a deeper discontinuity (~40 km) beneath the Moho which is possible evidence for underplating associated with Deccan age volcanism. Bird Island (Moho~18 km) and Desroche (Moho~23 km) show signs of being situated on islands above the transition from continental to oceanic crust. Alphonse, Coetivy and Platte all show receiver functions expected for oceanic crust, with Moho depths ~10 km. Inter-station phase velocity inversions from surface waves support these results with paths sampling the plateau region showing dispersion curves expected for continental crust, and those travelling between stations off the plateau showing evidence for oceanic crust. A deeper arrival is observed on the plateau stations at ~7 s or ~65 km. This feature is also seen in wide-angle controlled source work and the inter-station phase velocity inversions. Candidate interpretion for this Hales discontinuity include a Precambrian suture assoicated with shallow subduction or a shear-zone assoicated with deformation during breakup. Either feature may have influenced plume-related breakup in the region.
DE: 8104 Continental margins: convergent
DE: 8109 Continental tectonics: extensional (0905)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: Fall Meeting 2005