HR: 1330h
AN: T12A-0441    [PDF]
TI: Preliminary Insights to the Crust and Upper Mantle Structure of the northern Seychelles Continental Margin.
AU: * Sansom, V
EM: victoria.sansom@imperial.ac.uk
AF: Dept. of Earth Science and Engineering, Imperial College, RSM Building, Prince Consort Road, London, SW7 2BP United Kingdom
AU: Collier, J S
EM: jenny.collier@imperial.ac.uk
AF: Dept. of Earth Science and Engineering, Imperial College, RSM Building, Prince Consort Road, London, SW7 2BP United Kingdom
AU: Minshull, T A
EM: tmin@soc.soton.ac.uk
AF: School of Ocean and Earth Sciences, Southampton University, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Whitmarsh, R B
EM: rbw@soc.soton.ac.uk
AF: School of Ocean and Earth Sciences, Southampton University, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Kendall, M J
EM: kendall@earth.leeds.ac.uk
AF: School of Earth Sciences, Leeds University, The University, Leeds, LS2 4DW United Kingdom
AU: Lane, C I
EM: cil1@soc.soton.ac.uk
AF: School of Ocean and Earth Sciences, Southampton University, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Ryberg, T
EM: trond@gfz-potsdam.de
AF: GeoForschungsZentrum, Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Rumpker, G
EM: rumpker@gfz-potsdam.de
AF: GeoForschungsZentrum, Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AB: Marine geophysical profiles were collected over the conjugate Seychelles - Laxmi Ridge pair of rifted continental margins during Charles Darwin cruise 144 in Jan/Feb 2003. The aim was to obtain data from an initially fast-spreading rift (half rate 59 mm/yr) to constrain modelling of strain rate and its effect on passive margin structure. The margins were restored using seafloor spreading isochrons and a single transect was designed across the entire reconstructed rift avoiding fracture zones and seamounts. Here we present preliminary results from the Seychelles margin. The Seychelles islands consist principally of pre-Cambrian granite surrounded by a carbonate platform. The transect extends north of Mah\'{e}, over the shallow water plateau and into the deep-water Eastern Somali Basin (1.5-5$\deg$S, 55-57.5$\deg$E). The line extends beyond magnetic anomaly A27 onto undisputed oceanic crust. Wide angle and multi-channel seismic (MCS) data were obtained along a 300 km NNE/SSW line, and an additional 800 km of MCS data were also collected in the area. These MCS profiles were acquired using a 96-channel, 2.4 km-long streamer and a 6920 cu in airgun array fired every 60 s for the main line and a 3890 cu in, 30 s array for the extra MCS lines. 32 GEOMAR OBS were deployed along the main line and 21 Leeds/Potsdam land seismometers on the islands for the wide-angle work. Gravity, magnetics, swath bathymetry and dredge samples were also collected. The Moho is widely imaged on brute stacks of the MCS profiles beneath the deep-water part of the transect. Its character changes from flat and smooth on the ocean side to a more complex and layered form towards the continent. The crustal thickness appears to thicken from about 6 km to 14 km over a horizontal distance of 8 km, before the Moho image is lost beneath the rough platform edge. A narrow package of seaward-dipping reflectors is evident under sediments off the edge of the platform with 15-20$\deg$ dip and 16 km length. Several prominent seamounts were imaged using swath bathymetry within the ocean-continent zone. Three of these were dredged, and yielded basalts erupted from shallow marine or subaerial environments. The wide-angle data, from both OBS and landstations, recorded Pn arrivals at the furthest distance possible (300 km). First arrival travel times were picked and used in FAST to create a preliminary velocity model of the continental margin.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 7205 Continental crust (1242)
DE: 8010 Fractures and faults
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting