THE HATTON BASIN AND CONTINENTAL-MARGIN - CRUSTAL STRUCTURE FROM WIDE-ANGLE SEISMIC AND GRAVITY-DATA

Results from a wide-angle seismic and gravity study between the Rockal l Bank and the Iceland Basin in the North Atlantic are presented. Crus tal and sedimentary structures are resolved in the Hatton Basin and ac ross the Hatton continental margin (HCM) east of magnetic anomaly 24. The structure of the oceanic crust west of the anomaly is also determi ned. Gravity data support the seismic model in areas of good seismic c overage and are used to control the model where the wide-angle seismic data are poor. A two-layer sedimentary sequence is present both in th e Hatton Basin and across the continental margin. The lower layer, wit h P wave velocity of about 4 km/s, is interpreted as pre-Eocene synrif t sediments and is up to 3.5 km thick. A younger and thinner (1-2.5 km ) postrift sequence, with a velocity of about 2 km/s, defines a strong velocity contrast, which suggests an erosibnal unconformity surface. The sedimentary structure is distinctly different from that in the Roc kall Trough, where a third intermediate layer (V-p approximate to 3 km /s) occurs. The three-layer crust, characterized by two intracrustal r eflections (PiP1 and PiP2) varies from 30 km thick under the Rockall B ank to about 15 km below the Hatton Basin, where it is stretched by a factor of 2 relative to onshore Ireland. The crust is thinnest below t he Hatton Bank, where the presence of a single intracrustal reflection indicates that the lower crustal layer thins to below the seismic res olution limit. Below the HCM a region of thick lower crust with anomal ously high velocity (V-p approximate to 7.2 km/s) is resolved by the s eismic and gravity data. It is connected (west of anomaly 24) to a reg ion of oceanic crust, which is thicker than in the Iceland Basin. Thes e relationships between the thick lower crust below the HCM and the oc eanic crust in the Iceland Basin are interpreted as evidence for magma tic underplating, consistent with previous models for the HCM. The inf erred unconformity surface between the synrift and postrift layers may be due to regional uplift driven by upwelling of hot asthenosphere be fore anomaly 24 (early Eocene) time.