CRUSTAL STRUCTURE OF THE NORTHERN PART OF THE VORING BASIN, MID-NORWAY MARGIN, FROM WIDE-ANGLE SEISMIC AND GRAVITY-DATA

Three regional Ocean Bottom Seismograph (OBS) profiles with a total of fifteen recovered OBSs were acquired in the northern part of the Vori ng Basin, mid-Norway margin, in 1996. The data have been modelled by i nversion and forward modelling of the OBS vertical components (P-waves ). The velocity is found to increase downwards within the sedimentary layers, due to increasing depth of burial (confining pressure). Within the two deepest sedimentary layers there seems to be an increase of 0 .5-1 km/s in velocity northwestwards. This increase is most likely cau sed by high-velocity sill-intrusions in the sedimentary rocks, emplace d during the rift episode leading to Early Eocene opening of the NE At lantic. The presence of significant amounts of sills seems to terminat e close to the Nyk High along profile 5 (dip-profile), and close to a dome northwest of the shelf edge along profile 6 (dip-profile). The ve locity in the top of this dome is anomalously high (3.4 km/s at only 1 km depth beneath the seafloor), suggesting that the high consists of volcanic rocks, or heavily intruded sedimentary rocks. The relatively low velocities derived from within the upper crystalline crust (5.9-6. 2 km/s) confirms that the crust is of continental origin. Within the l ower crust there seems to be a clear increase in velocity northwestwar ds (from about 7.0 km/s to about 7.4 km/s), suggesting that the amount of high-velocity intrusions (underplating) in the lower crust decreas es landwards. The modelling of the strike-profile (profile 7) suggests that the transition from a lower crust dominated by magmatic intrusio ns to a more undisturbed continental lower crust is located approximat ely beneath this profile. The model for profile 7 ties closely southwe stwards to the models derived from OBS data acquired in 1992, and nort heastwards to Lofoten (OBS data acquired in 1988). The models indicate that the thick magmatic intrusions in the sedimentary rocks and lower crust extend further landwards in the area of the 1992 survey, and th at the transition zone is related to the Suit Lineament, The distribut ion of magmatic rocks thus seems to correlate strongly with pre-breaku p structures. In addition to the P-wave modelling, gravity modelling h as been performed along all profiles. The gravity modelling confirmed all main aspects of the OBS models, and provided constraints on the cr ustal structures towards the ends of the profiles. (C) 1998 Elsevier S cience B.V. All rights reserved.