LUNDIN, E.R., A.G. DORÉ, A. GRØNLIE, Statoil

Abstract: Mid-Cenozoic post-break up deformation in the "passive margins" bordering the Norwegian-Greenland Sea: implications for HC exploration

Significant post-break up compression, extension, and magmatism is documented in the margins surrounding the Norwegian and Greenland Seas (Fig. 1). The deformation is attributed to: 1) a major mid-Cenozoic plate reorganisation and associated change in extension direction, initiated approximately at Chron 13 (35 Ma), and 2) seafloor spreading influenced by the Iceland hotspot.

As a consequence of the change in plate motions, a northward propagating rift axis developed within East Greenland, and led to development of the Kolbeinsey Ridge between Liverpool Land and the Jan Mayen microcontinent. A significant number of igneous centeres of mid-Cenozoic age are documented onshore East Greenland, and several are interpreted from aeromagnetic data offshore. This magmatism is presumed associated with the extension preceeding spreading.

Along the SW Barents Sea shear margin the new plate motion terminated the West Spitsbergen Orogeny, separated the Hovgård Ridge microcontinent from the Svalbard Platform, and transformed the shear margin into an oblique rift margin.As a consqeuence of oblique rifting the Knipovitch Ridge developed. The change in plate motions resulted in rifting and associated magmatism in the Sørvestnaget Basin and Vestbakken Volcanic Province. Extensional deformation and magmatism is postulated along much of the Norwegian margin south-east-wards to and including the Lofoten margin, and into the northern Vøring Basin.

Interpretation of magnetic data suggests that the West Jan Mayen Fracture Zone has an eastern "counterpart" continuing from the Mohns Ridge to the Bivrost Lineament of the Norwegian margin. If so, the extension in East Greenland can be kinematically linked with the extension along the mid-Norwegian and SW Barents Sea margins.

Mid-Cenozoic compressional doming, reverse faulting, and broad basin inversion is found in the margins surrounding the Norwegian-Greenland Sea.Within the NW European margin the compression is constrained to the deep Cretaceous depo-centres. The reason for the preferred location of compression in these deep rift axes is presumed to be related to a rift-induced crustal weakness. Within the Norwegian margin, the domes appear to become younger northward (Fig. 2), and are suggested to be genetically linked with ridge-push forces from the northward propagating Kolbeinsey Ridge. Domes in the Rockall-Faroes area are distributed in an arc-shaped pattern, and could relate to a radial push from the Iceland Hotspot. The hotspot is expected to have enhanced the ridge push forces of the region in general and is, therefore, considered to be an important element in the compressional deformation.

Post-break up compression formed some of the most attractive structural traps in the Norwegian frontier area (Vøring and Møre Basins). To date this playtype has resulted in one major success, the c. 12 TCF Ormen Lange gas discovery. A presumed landward extension of the East Jan Mayen Fracture Zone separates the Ormen Lange Dome into a southerly and a northerly part, where the southern part contains the gas accumulation while the northern part is dry. It is not known if the dry portion of the dome is a function of reservoir distribution or fault seal. If the latter, it could stem from mid-Cenozoic reactivation.

Post-breakup extension generated uplift, erosion, and related depositional systems. The large Nyk High fault block in northern Vøring Basin was uplifted and breached (Fig. 3)..Breaching of this major structure would have caused loss of any previous accumulation of hydrocarbons. Due to minimal subsequent sedimentation, the high remains breached at present. The c. 1 TCF gas discovery in PL 218 on the Nyk High lies within structural closure of a "small" independent structure on the flank of the major high and was thus not affected by the breaching. A more general effect of ridge push is the rotation of the stress system. Prior to breakup the margin experienced margin-perpendicular extension while following breakup the margin was subject to margin-perpendicular compression. This change in the stress field would have influenced fluid flow, and is speculated to have been an element in remigration of hydrocarbons.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England