HR: 11:50h
AN: T32A-07    [Abstracts]
TI: Crustal structure of the northern Seychelles margin: Evidence for restricted magmatism during breakup
AU: * Collier, J S
EM: jenny.collier@imperial.ac.uk
AF: Department of Earth Science & Engineering, Imperial College London, Prince Consort Road, London, SW7 2AZ, United Kingdom
AU: Minshull, T A
AF: School of Ocean and Earth Science, University of Southampton, National Oceanographic Centre, Southampton, SO14 3ZH, United Kingdom
AU: Kendall, M K
AF: Department of Earth Sciences, Bristol University, Queens Road, Bristol, BS8 1RJ, United Kingdom
AU: Whitmarsh, R B
AF: School of Ocean and Earth Science, University of Southampton, National Oceanographic Centre, Southampton, SO14 3ZH, United Kingdom
AU: Hammond, J O
AF: Department of Earth Sciences, Bristol University, Queens Road, Bristol, BS8 1RJ, United Kingdom
AU: Lane, C I
AF: School of Ocean and Earth Science, University of Southampton, National Oceanographic Centre, Southampton, SO14 3ZH, United Kingdom
AU: Sansom, V
AF: Department of Earth Science & Engineering, Imperial College London, Prince Consort Road, London, SW7 2AZ, United Kingdom
AB: We present a model of the structure of the northern Seychelles continental margin derived from wide-angle seismic travel-time inversion, teleseismic receiver functions and potential field data. Break-up occurred 2.5 Ma after, and 1000 km to the west of, the emplacement of the Deccan Traps. However, despite this spatial and temporal closeness, we do not find the typical set of geophysical characteristics reported at other volcanic rifted margins associated with continental flood basalts, such as those of the north Atlantic. The oceanic crust formed during the first 3 Ma of seafloor spreading is just 5 km thick, less than half that seen at some other volcanic margins. The continent-ocean transition itself is narrow and whilst two packages of seaward-dipping-reflectors are imaged they are weakly developed. Within the transitional lower crust there is a region of high-velocity material (7.5-7.7 km/s) directly below the inner seaward dipping reflector package that we interpret as an intruded body of mafic material, but it is small, just 10 km wide by 4 km thick. However a much more extensive area of probable mafic material (130 km wide and 6 km thick) is present beneath the entire stretched continental crust and part of the unstretched Seychelles Plateau. A similar pattern of underplated material beneath the stretched continental portions, but limited magmatism in the actual break-up zone and thin earliest oceanic crust, is also seen on the conjugate-Indian (Laxmi Ridge) margin. Together with the known ages of volcanic products from the Seychelles Plateau, we conclude that the underplating of the continental portions pre-dates the rifting, and that break-up between India and the Seychelles was characterised by a lack of excess volcanism. We suggest that the underplating event dehydrated, and hence increased the solidus of, the underlying mantle, such that the subsequent Seychelles-India separation, despite elevated temperatures did not generate excess volcanism. We conclude that tectonic history as well as mantle temperature can determine the degree of magmatism during continental break-up
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting