HR: 1340h
AN: T43B-1403    [Abstracts]
TI: Crustal Structure of the Continental Margin Offshore French Guiana, Central Atlantic
AU: * Greenroyd, C J
EM: christopher.greenroyd@durham.ac.uk
AF: University of Durham, Department of Earth Sciences, South Road, Durham, DH1 3LE United Kingdom
AU: Peirce, C
EM: christine.peirce@durham.ac.uk
AF: University of Durham, Department of Earth Sciences, South Road, Durham, DH1 3LE United Kingdom
AU: Rodger, M
EM: matthew.rodger@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences, Parks Road, Oxford, OX1 3PR United Kingdom
AU: Watts, A B
EM: tony@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences, Parks Road, Oxford, OX1 3PR United Kingdom
AU: Hobbs, R W
EM: r.w.hobbs@durham.ac.uk
AF: University of Durham, Department of Earth Sciences, South Road, Durham, DH1 3LE United Kingdom
AB: During November/December 2003 we carried out a marine geophysical survey of the continental margin offshore French Guiana onboard RRS Discovery. The survey included 425 line km of coincident multi-channel seismic (MCS) reflection and wide-angle seismic refraction data which were acquired along a transect of the margin. In addition, gravity and magnetic anomaly data were acquired. Modelling of wide-angle refraction data from 19 ocean bottom seismographs (OBSs) and 5 land-based seismographs, has revealed a P wave velocity model of the crustal and mantle structure of the margin between the Demerara Plateau and the Amazon Fan. The model is generally well constrained within experimental errors and is consistent with coincident MCS data and gravity modelling. The model reveals a thick continental crust, with a maximum thickness of 33-37 km, which thins by a factor of ~6 over a distance of ~70 km, with no significant evidence for faulted and/or rotated block structures. The thinned continental crust is separated from thin (~3.5-5 km) but relatively uniform oceanic crust, with P wave velocities in layer 2 between 4.1 and 5.7 kms^-1 and in layer 3 between 6.4 and 7.5 kms^-1, by a 40 km wide ``transition zone''. The abrupt crustal thinning, wide transition zone and lack of either seaward-dipping reflectors or magmatic underplating suggest that the margin offshore French Guiana is a non-volcanic oblique transform-type margin that formed following the separation of the South American and African plates during the opening of the Equatorial Atlantic ocean. Our results of seismic and gravity modelling have implications for the early opening history of the Equatorial Atlantic ocean and the structure and evolution of both its rift- and transform-type margins.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935, 7294)
DE: 8106 Continental margins: transform
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 9325 Atlantic Ocean
SC: Tectonophysics [T]
MN: Fall Meeting 2005