Quantifying the contribution of tectonics vs. differential compaction in the development of domes along the Mid-Norwegian Atlantic margin M. Go ´mez and J. Verge ´s Group of Dynamics of the Lithosphere, Institute of Earth Sciences‘‘Jaume Almera’’, CSIC, Barcelona, Spain ABSTRACT A sequential restoration based on combined backstripping and unfolding methods a¡ords the opportunity to study the Cenozoic evolution of two low amplitude domes in the Mid-Norwegian extensional margin, the Helland Hansen Arch and the Vema Dome.The integration of growth strata geometries observed in both £anks of the domes demonstrate that the structures grew by a variable combination of tectonics and di¡erential compaction mechanisms. Sequential restoration shows that the Helland Hansen Arch grew between Early Oligocene and earliest Late Pliocene times (33^1.9 Ma). During the ¢rst phase of growth (33^9 Ma), the tectonic compression accounted for a minimum of 27% of the total dome amplitude. During Late Miocene to Pliocene times (9^1.9 Ma), di¡erential compaction was the mechanism for dome growth. During Late Pliocene times, the Helland Hansen Arch grew with the highest rates coinciding with initial deposition of prograding wedges (3.6^1.9 Ma). In contrast, the Vema Dome started to develop in Early Eocene times and grew at a fairly constant rate up to Early Pliocene times at 3.6 Ma.The ampli¢cation of the Vema Dome took place through both di¡erential compaction and tectonics between Early Eocene and Late Miocene times (54.8^7 Ma).The tectonic contribution accounted for a minimum of a 37% of the total dome amplitude. During Pleistocene times, the progradation of clastic wedges led to a decrease of the amplitudes of both the Helland Hansen Arch and the Vema Dome.The di¡erent timing of tectonic growth for analysed domes and arches suggest that a small and protracted phase of compression a¡ected the Mid- Norwegian Margin.This agrees with well-known widespread contractional deformation a¡ecting the Atlantic Margin of the European Plate during theTertiary. INTRODUCTION Tectonic inversion of thick sedimentary basins is one of the most common structural processes a¡ecting pre- viously extended continental margins (Cooper et al., 1989), (Fig. 1). The inversion of a thick post-rift basin with syn- cline geometry smoothes the syncline below the null point and creates a dome above it (Fig.1a). Another doming me- chanism is the di¡erential compaction operating above structural highs separating two adjacent basins.The high sediment load in the basins implies that more compaction occurs in the basins than in the neighbouring structural highs, which are characterised by a thinner sedimentary in¢ll. The resultant geometry after compaction consists of synclines along the axis of the basins and anticlines above the structural highs (Fig. 1b). A third mechanism is caused by the progradation of large sedimentary wedges that produce deformation below, and in front of the pro- grading units. The load of thick wedges also generates a considerable amount of isostatic subsidence, which com- binedwith previous depositional slopes can lead to the for- mation of anticlinal highs (Stuevold et al., 1992; Kjeldstad et al., 2003) (Fig. 1c). The Mid-Norwegian Margin is characterised by the presence of large-scale domes and elongated arches with a low amplitude/wavelength ratio (0.02).These structures formed after the continental break-up, at the Palaeocene^ Eocene transition, and are aligned following an approxi- mate N^S direction oblique to the main NE^SW trend of the margin (Fig. 2).The domes and arches of the Mid-Nor- wegian Margin have been primarily interpreted as inver- sion structures because of intraplate compressive stresses (Bukovics & Ziegler, 1985; Blystad et al., 1995; Dore¤ & Lun- din, 1996; VÔgnes et al., 1998). Analogous Cenozoic com- pressional folding has been reported along o¡shore basins in the continental margins of the North Atlantic domain, (Wof British Isles (Roberts, 1989), Faroe Island area (Bol- dreel & Anderson, 1993) and also along onshore basins (WessexBasin (Underhill & Paterson,1998)). Nevertheless, the formation of domes by compression in the Norwegian Correspondence: Jaume Almera, Institute of Earth Sciences, CSIC, Lluis Sole¤ i Sabar|¤s s/n, 08028 Barcelona, Spain. E-mail: jverges@ija.csic.es Basin Research (2005) 17, 289–310, doi: 10.1111/j.1365-2117.2005.00264.x r 2005 Blackwell Publishing Ltd 289