CRUSTAL STRUCTURE OF THE GOBAN SPUR RIFTED CONTINENTAL-MARGIN, NE ATLANTIC

We present results that constrain the crustal structure across a typical 'non-volcanic' rifted continental margin, the Goban Spur in the NE Atlantic. Traveltime and amplitude modelling of wide-angle ocean-bottom seismograph profiles shows that the continental crust thins in a seaward direction to about 7 km before it breaks to allow a new oceanic spereading centre to develop. The crustal-velocity structure, the stretching factors and the density distribution inferred from gravity anomalies are consistent with bulk pure shear stretching for the development of the rifted continental margin. The seismic-velocity structure of the thinned continental crust suggests that thinning was accompanied by only limited igenous intrusion and extrusion in the upper crust. The adjacent oceanic crust is abnormally thin (5.4 km). This is explained most readily by accretion at a very slow spreading centre (approx 11 mm yr-1 full rate), although additional cooling by conductive heat loss from the parent mantle as it rose slowly beneath the stretched and thinned continental lithosphere, together with minor igenous intrusion into, and surface flows onto, the adjacent continental crust may also have reduced the oceanic igenous thickness immediately adjacent to the continent-ocean transition.