Journal of the Geological Society, London, Vol. 160, 2003, pp. 197–208. Printed in Great Britain.

197

Extension, crustal structure and magmatism at the outer Vøring Basin, Norwegian

margin

L. GERNIGON 1, J. C. RINGENBACH 2, S . PLANKE 3, B. LE GALL 1 & H. JONQUET-KOLSTØ 4

1Institut Universitaire Europeen de la Mer, Place Nicolas Copernic, 29280 Plouzane, France

(e-mail: gernigon_geol@hotmail.com)2TotalFinaElf Exploration Libya, Dhat El Imad building, tower 3, P.O Box 91171, Tripoli, Libya

3Volcanic Basin Petroleum Research (VBPR), Forskningsparken, Gaustadalleen 21, N-0349 Oslo, Norway4TotalFinaElf Exploration Norge AS, P.O. Box 168, 4001 Stavanger, Norway

Abstract: Regional analysis of new 2D and 3D multichannel seismic data has improved interpretation of the

crustal configuration and structural style along the Norwegian margin. Five domains with different structural

styles and evolutions are defined along the outer Vøring Basin: (1) the Nyk High–Naglfar Dome; (2) the

north Gjallar Ridge; (3) the Gleipne saddle; (4) the south Gjallar Ridge; (5) the Ran ridge. Early Campanian–

Early Paleocene and Early to mid-Cretaceous extensional events are evidenced. Timing of deformation and

structural styles observed along each segment reflect a lateral variation of the rifted system, probably affected

by magma-tectonic processes. Correlation with the deep structures of the outer Vøring Basin shows that the

shallow structure in that basin is directly controlled by a deep-seated, strong, high-amplitude reflection (the T

reflection), marking the top of a high-velocity body (Vp .7 km s�1). The relation between the lower-crustal

architecture and the subsurface basin structures has implications for the margin evolution and for the nature of

the high-velocity body.

Keywords: Norwegian margin, rifting, magmatism, underplating.

The Norwegian margin is part of the NE Atlantic rift system

(Fig. 1). It is characterized by a long period of episodic rifting

initiated after the Caledonian orogeny (Dore et al. 1999; Brekke

2000; Brekke et al. 2001). The overall tectonic framework of the

margin between 628 and 698N consists of a central NE-trending

deep Cretaceous basin (the Vøring and Møre basins), flanked by

palaeo-highs, platforms and the elevated mainland (Blystad et al.

1995).

In a regional context, the Trøndelag Platform and the Halten

Terrace, to the east (Fig. 3), are the best areas to illustrate the

Jurassic evolution, which was strongly influenced by Triassic salt

tectonics resulting in the development of both low-angle detach-

ment and steeply dipping fault structures (Koch & Heum 1995;

Pascoe et al. 1999). A major unconformity at the base of the

Cretaceous marks the Late Jurassic–Early Cretaceous rifting

episode, which is commonly considered as the major rifting

event in the Halten Terrace (Blystad et al. 1995). Although not

proven by well control, the Triassic–Jurassic sediments may be

present below the thick Cretaceous series in the central Vøring

Basin and in the outer Vøring Basin (Blystad et al. 1995). The

Cretaceous evolution of the Norwegian margin is also a subject

of debate. Dore et al. (1999) proposed separate Late Jurassic and

Cretaceous rift episodes in the Vøring Basin, whereas Blystad et

al. (1995) and Brekke (2000) argued for a continuous rift episode

from Mid-Jurassic to Early Cretaceous time. According to Pascoe

et al. (1999), extension in the northern part of the Halten Terrace

continued until Late Aptian to Early Cenomanian time.

The previous structural works described the outer Vøring

Basin mainly in the northern part (Skogseid & Eldholm 1989;

Lundin & Dore 1997; Mogensen et al. 2000) or discussed the

Gjallar Ridge in detail (Ren et al. 1998) but few studies were

performed in the southern part. Several regional reviews and

modelling studies of the Norwegian margin have been published

(Eldholm et al. 1989; Skogseid 1994; Blystad et al. 1995; Koch

& Heum 1995; Bjørnseth et al. 1997; Robert et al. 1997; Walker

et al. 1997; Hjelstuen et al. 1999; Brekke 2000; Tsikalas et al.

2001), but few structural studies have focused on the early rifting

evolution and the structure of the outer Vøring Basin, investi-

gated in this paper (Figs 1 and 3).

The outer Vøring Basin consists of a NE-trending system of

ridges generally assigned to a Maastrichtian–Paleocene episode

(Lundin & Dore 1997; Ren et al. 1998) or to an Early

Cenomanian–Paleocene rifting event (Bjørnseth et al. 1997)

(Fig. 1). It is overlain to the west by Tertiary flood basalts

(seaward-dipping reflectors) extruded before and during the

continental break-up in a short period of time (63–54 Ma)

(Saunders et al. 1997). Before this volcanic event, a regional

uplift close to the Cretaceous–Tertiary boundary is observed

along the North Atlantic rift system and is interpreted to reflect

interaction of the Iceland mantle plume with the base of the

lithosphere (Dam et al. 1998; Skogseid et al. 2000).

The outer Vøring Basin is also an interesting area for

investigating the relationships and interactions between crustal

magmatism and basin deformation in space and time. Large

amounts of seismic refraction and reflection data have greatly

improved knowledge of the crustal structure along the outer

Vøring Basin and the Vøring Marginal High (Mutter et al. 1984;

Planke et al. 1991; Skogseid et al. 1992; Eldholm & Grue 1994).

Commonly observed below the margin, a high P-wave velocity

body (Vp .7 km s�1) (lower-crustal body) is interpreted as

homogeneous, underplated mafic crust associated with perva-

sively intruded crust (White & McKenzie 1989; Mjelde et al.

1997; Eldholm et al. 2000). Previous studies have pointed out

the isostatic impact of the lower-crustal body on the subsidence

of the margin (Skogseid 1994; Robert et al. 1997; Walker et al.

1997). At the mid-crustal scale, Lundin & Dore (1997) inter-

preted the geometry of the Late Cretaceous–Paleocene normal

faulting along the Gjallar Ridge as a mid-Cretaceous to Paleo-

cene metamorphic core complex caused by magmatism at the

base of the crust.

This paper is a regional overview of the entire outer Vøring

Basin with broader implications for the deformation of rifted

systems and/or the development of volcanic margins. The aims

of this study are: (1) to constrain and refine the structural and

stratigraphic history of the outer Vøring Basin; (2) to describe

the along-strike structural variation of the sub-basins and their

genetic relationships with the deep crustal geometry; (3) to

attempt to document the variability of the structural styles and

their links with the Tertiary magmatism or/and the structural

inheritance. Because the official nomenclature proposed by

Blystad et al. (1995) is not sufficiently detailed to describe the

structural complexity of the outer Vøring Basin, additional

informal names are proposed for specific structures (Table 1).

Data, methods and interpretation confidence

This work is mainly based on the interpretation of a regional

database of more than 100 000 km of 2D seismic reflection, at

2 km 3 1 km spacing, tied to wells on the Trøndelag Platform

and to some released information from recent wells in the Møre

and Vøring basins. Three-dimensional seismic reflection data are

also used, particularly a 3D seismic survey covering the northern

part of the Gjallar Ridge (Fig. 1). Interpretation was carried out

within a single GeoframeTM project covering the region between

628N and 688N, and was undertaken in the framework of the

preparation of the 16th Norwegian concession round (2001).

Compilation of proprietary ship track (Norwegian Petroleum

Directorate (NPD) database and TGS-NOPEC surveys V2R96,

MWT96, HT97, KFW98 and RSW98) and public gravity data

(Sandwell & Smith 1997) are also used and correlated with the

regional structure.

The Early and pre-Cretaceous markers are calibrated with the

numerous Halten Terrace exploration wells but the pre-Turonian

basin history of the outer Vøring Basin is mostly based on

seismic interpretation. In addition to Deep Sea Drilling Program

(DSDP) and Ocean Drilling Program (ODP) data (Eldholm et al.

1989; Hjelstuen et al. 1999), released data from recently drilled

wells (Fig. 1) on the Nyk High (6707/10-1) (e.g. Kittilsen et al.

1999), Vema Dome (6706/11-1), north Gjallar Ridge (6704/12-1)

and Helland Hansen Dome (6505/10-10) supply further calibra-

tions. Wells 6707/10-1 and 6706/11-1 are drilled on a structural

high position and do not penetrate the lower section of the synrift

sequence below the Coniacian–Turonian series. The Gjallar well

(6704/12-1) reached the Lower Campanian series. Around the

south Gjallar and Ran ridges, the interpretations rely mostly on

regional correlations of seismic facies.

Fig. 1. Structural map of the outer Vøring Margin and location of regional cross-sections in Figure 8. BCU, base Cretaceous unconformity; BL, Bivrost

Lineament; FFC, Fles Fault Complex; FG, Fenris Graben; GFZ, Gleipne Fracture Zone; GS, Gleipne saddle; HG, Hel Graben; HT, Halten Terrace; JMFZ,

Jan Mayen Fracture Zone; ND, Naglfar Dome; NGR, north Gjallar Ridge; NH, Nyk High; NS, Nagrind Syncline; RaB, Ran basin; RR, Ran ridge; Rym

FZ, Rym Fault Zone; SGR, south Gjallar Ridge; TP, Trøndelag Platform; VD, Vema Dome; VMH, Vøring Marginal High; VS, Vigrid Syncline. Volcanic

facies map of the Vøring Marginal High has been modified after Berndt et al. (2001).

L. GERNIGON ET AL .198

Table 1. Characteristics of the outer Vøring Basin

Structural element Main geological features Deep reflections Ages of the main tectonic events

Nyk High� NE-trending structural high Not observed? High-velocity sills Latest Cretaceous–PaleoceneHel Graben–NaglfarDome�

Cretaceous–Paleocene depocentreinverted during Tertiary. High positionduring the Maastrichtian

Poorly expressed. High-velocity sills Collapse during Paleocene

Inversion Early Eocene–PresentNorth Gjallar Ridgey Major tilted blocks affected by low-angle

faulting, partly controlled by a shaledecollement layer

The north Gjallar Ridge is influenced bythe dome-shaped T reflection (top of thehigh-velocity body (Vp .7.1 km s�1)

Early Campanian?– Paleocene

Fenris Graben� Graben onlapped by the inner flows.Located in the western part of the northGjallar Ridge and south Gjallar Ridgesegments

T reflection observed and expectedbelow the inner lava flows

Early Campanian–Paleocene

Gleipne saddley Synform, saddle structure, influenced bymagmatic sill injection. Minor faulting

Progressive plunging of the T reflection Early Campanian?– Early Paleocene

South Gjallar Ridgey Tilted panels controlled by step faultsconnected with Palaeozoic–Jurassicpanels

The T reflection observed in highposition

Early Campanian–Early Paleocene

Early–mid-CretaceousRan basiny Cretaceous depocentre influenced by

voluminous sill intrusion. Subaerialvolcanism is reduced compared withthe other sub-basins

Transition zone between the T reflectionand the top basement

Late Jurassic–mid-Cretaceous?

Early Campanian–Early PaleoceneRan ridgey Uplifted Triassic–Jurassic depocentre

sealed by the base Cretaceousunconformity. Tilted panels controlledby a decollement layer

Top faulted basement correlated withthe T reflection

Late Jurassic–mid-Cretaceous?

Early Campanian–Early Paleocene

�Nomenclature after Blystad et al. 1995.yInformal names used in this paper.

Fig. 2. Bouguer residual gravity anomaly

map, 50 km high-pass filtered (courtesy of

TGS NOPEC/VBPR). Abbreviations as in

Figure 1. Numbers represent the location of

the five domains.

VØRING BASIN, NORWEGIAN HIGH 199

Structure and evolution of the outer Vøring Basin:evidence for along-strike variation

Gravity data

The 50 km high-pass filtered Bouguer residual gravity anomaly

map of the outer Vøring Basin shows various trends and

structures (Fig. 2). Negative anomalies are found to be consistent

with the sub-basins, whereas positive anomalies reflect the

structural highs and lows mapped in this study (Figs 1 and 4).

The complex pattern of gravity anomalies can be used together

with the structural map to define five structural domains,

comprising from north to south: (1) the Nyk High–Hel Graben

domain, with a NE–SW positive anomaly for the Nyk High and

a north–south to NE–SW negative trends for the Hel Graben;

(2) the north Gjallar Ridge domain, bounded to the north by the

Rym Fault Zone and showing a main positive rounded anomaly;

(3) the Gleipne saddle domain, characterized by a gravity low;

(4) the south Gjallar Ridge domain, marked by a broad NE–SW-

trending positive anomaly, adjacent to a negative anomaly

situated below the inner lava flows; (5) the Ran ridge domain,

with NW–SE and east–west orientations located in the prolonga-

tion of the oceanic Jan Mayen Fracture Zone that also coincides

with major NW–SE positive trends in the oceanic domain

(Fig. 3).

The five domains coincide with high or low structures

characterized by a gradual along-strike variation without any

clear boundaries. Nevertheless, approximate limits can be pro-

posed to better define the five zones or domains (Fig. 4),

illustrated below by a summary of their tectonostratigraphic

evolution (Fig. 5) and detailed geoseismic profiles (Fig. 8).

Nyk High–Hel Graben

The morphology of this segment is dominated by the Nyk High,

which separates the Nagrind Syncline from the Hel Graben (Fig.

6a). The Nyk High is bounded to the west by a major normal

fault complex whereas the Hel Graben has subsequently been

inverted to form the Naglfar Dome (Fig. 1). The Nyk High is,

together with the Gjallar Ridge and the Vema Dome, one of the

few structures recently drilled in the Vøring Basin. The Nyk

High is a large SE-tilted faulted block affected by an array of

Early Campanian–Early Paleocene, NW-dipping normal faults.

The normal faults are interpreted to detach at depth in Lower

Cretaceous(?) shales and they appear to be located above faulted

blocks of similar polarity at base Cretaceous level.

Well 6707/10-1 was drilled in a faulted block SE of the Nyk

High and bottomed in Santonian strata. The constant thickness of

the Turonian–Santonian series and their apparent continuity

towards the Hel Graben suggest minor south-dipping normal

faulting before the Early Campanian in the Hel Graben (Fig. 8a).

In the northern prolongation of the Nagrind Syncline, the Nyk

High probably remained unfaulted until Late Maastrichtian time

during the deposition of the thick Nise formation sand in

Santonian–Early Campanian time. As interpreted here, the uni-

form thickness of the Upper Cretaceous seismic package sug-

gests also that most of the tilting and uplift of the Nyk High

occurred during the Late Paleocene–Eocene (Fig. 5).

At 10–20 km west of the Nyk High, the Cretaceous basin was

mainly eroded during Maastrichian to Early– (mid?)-Paleocene.

During this period, the uplifted and eroded area represented the

Fig. 3. Regional cross-section of the Vøring margin from the Vøring

Marginal High to the Trøndelag Platform. IF, inner flows; LF, landward

flows; SDR, seaward-dipping reflectors. Location is shown in Figure 1.

L. GERNIGON ET AL .200

highest position of the segment. Partly concomitant with the

uplift of the Nyk High, the structure of the Hel Graben and the

presence of Paleocene sediments above the base Tertiary uncon-

formity argue for a sudden collapse of the basin during the

mid?–Late Paleocene–Eocene, in agreement with Lundin &

Dore (2002). The mid–Late Paleocene deformation is coeval

with emplacement of high-velocity sills in the Hel Graben, which

is thus interpreted as a probable igneous centre during this period

(Berndt et al. 2000). The break-up magmatism is expected to be

involved in the sudden uplift of the Nyk High structure. By

analogy with structures deduced from sand–silicone models

(Bonini et al. 2001), a lateral flow and a boudinage of the melted

lower crust, triggered by underplated magma, may explain both

the Nyk High uplift and the Hel Graben collapse (Fig. 6). A

slightly different magma-tectonic model has been also proposed

by Lundin et al. (2002), who interpreted the Hel Graben as a

major cauldron that collapsed during Paleocene time.

North Gjallar Ridge

The north Gjallar Ridge domain represents the ridge itself and

part of the Fenris Graben (Figs 1 and 8b). The ridge is well

expressed at the base Tertiary level (Fig. 6) and it is mostly

dissected by arrays of NW-dipping faults (Figs 8b and 9). Strongly

truncated by the base Tertiary unconformity, above the circular-

shaped gravity high (Fig. 4), each block is characterized by well-

layered reflections that are interpreted as synrift deposits (Fig. 9).

Swieciki et al. (1998) proposed a Triassic–Jurassic age for these

deposits, but recent drilling and in-house dating show it to be of

Campanian–Maastrichtian age so that the Base Tertiary unconfor-

mity is assumed to represent a hiatus between Lower Maastrich-

tian and Upper Paleocene (or/and Lower Eocene) series.

Contrary to the models established by Walker et al. (1997) and

Ren et al. (1998), continuous detachment crosscutting the entire

upper crust is not observed and an intricate system of detachment

faults, controlling block rotation during the Atlantic rifting, is

mainly limited to the upper part of the basin (Fig. 9). In the

eastern limb of the ridge, strongly rotated small blocks are

observed above a chaotic transparent seismic facies, believed to

represent (middle?) Cretaceous mobile shales (Fig. 9). The

shales, interpreted to have acted as a decollement for the

overlying rollover feature, seem to die out laterally to the north,

where faults are steeper. The rollover structure predicts a

westward thickening of the synrift sequences and is at least

partly concomitant with onlap and pinch-out of Turonian–

Paleocene formations within the Vigrid Syncline on the eastern

flank (Fig. 8b). In the western part of the ridge, a sigmoidal fault

pattern at the base Tertiary unconformity level (Fig. 9) also

suggests dextral strike-slip deformation along NE-trending faults.

The Paleocene interval largely onlaps the north Gjallar Ridge

and thus was only slightly faulted in Early Paleocene to Early

Eocene time. Faulting along the ridge probably took place a few

million years before the break-up in the latest Paleocene; this

suggests a progressive focus of crustal deformation to the west

(e.g. Lundin & Dore 1997). The westward shift may be explained

by a weakening of the crust induced by the starting magmatism,

as has been proposed for the west Greenland margin, where the

pre-break-up deformation was progressively focused toward the

igneous centres (Geoffroy et al. 2001).

Fig. 4. Strike-parallel section along the Gjallar ridges and Naglfar Dome

illustrating the lateral evolution and corrugation of the T reflection (TR)

along the outer Vøring Basin and its relation to sill intrusions. Legend as

for Figure 3. Location is shown in Figure 1.

VØRING BASIN, NORWEGIAN HIGH 201

Gleipne saddle

The Gleipne saddle forms a transition zone between the north

and south Gjallar ridges (Figs 1 and 8c). At Cretaceous level, it

is characterized by an embayment NW of the Vigrid Syncline

(Fig. 1). As observed in Figure 4, the transition zone coincides

with both a marked gravity low and an offset of the Vøring

Escarpment (Fig. 1).

Faulting in the Gleipne saddle is not significant in comparison

with the north Gjallar Ridge and no major significant block

rotation is observed (Fig. 8c). However, seismic interpretation

within the saddle is rendered difficult by the presence of

numerous magmatic intrusions in the Cretaceous section. Never-

theless, the Cretaceous series appear to thicken from the north

Gjallar Ridge into the Gleipne saddle (Fig. 4).

During Early Paleocene–Mid-Eocene time, a sedimentary

wedge infilled westwards from the Vigrid Syncline into a large

part of the subsiding Gleipne saddle (Figs 4 and 8c). Moreover,

inner volcanic flows, emplaced during the break-up, flowed

around the north Gjallar Ridge and preferentially infilled the

southern part of the Fenris Graben (Fig. 1), hence suggesting its

low structural position with regard to the north Gjallar Ridge

(e.g. Lundin & Dore 1997).

South Gjallar Ridge

The south Gjallar Ridge lies between the Gleipne saddle and the

Ran basin (Figs 1 and 8d) and is bounded to the east by the

Fenris Graben. The structural history is not constrained by

proximate well control and is based only on regional seismic

facies correlation.

The south Gjallar Ridge is a prominent elongated high (75 km

3 50 km) at base Tertiary unconformity level. The south Gjallar

Ridge is expressed by steep NW-dipping normal faults bounding

elongated rotated blocks (Fig. 8d). The faulting activity is

assumed to be of Early Campanian–Early Paleocene age as

similarly stated for the north Gjallar Ridge. The structural style

suggests domino deformation rather than the listric faulting

evident in the north Gjallar Ridge. The layered seismic facies of

the synrift sediments are less well developed than in the north

Gjallar Ridge, whereas the faults show less displacement (Fig.

8). The Vigrid Syncline to the east is marked by Early Cretac-

eous faulting, sealed near the base Cenomanian level (Fig. 8d).

The gravity low, observed in the western part of the segment,

is inferred to correspond to the progressive down-faulting of the

Cretaceous basin in the Fenris Graben. However, this area is

poorly imaged because of the emplacement of the inner lava

flows (Fig. 8d).

Ran ridge

The Ran ridge is the southwesternmost domain of the outer

Vøring Basin and appears to be different from the other ridges

(Figs 1 and 8e). The domain is composed of the Ran ridge and is

Fig. 5. Tectonic calendar of the Vøring margin. Time scale after Berggren et al. (1995).

L. GERNIGON ET AL .202

bounded by the Ran basin to the west and lies to the SE of the

Jan Mayen Fracture Zone (Fig. 1). A significant part of the Ran

ridge lies beneath the inner flows to the west and numerous

intrusions affect the Cretaceous and older series (Fig. 8e).

The axis of the Ran ridge is shifted eastwards relative to the

Gjallar ridges (Fig. 1). On its eastern flank, the Ran ridge is

defined by a clear unconformity, not yet drilled but interpreted to

be the base Cretaceous unconformity. The feature is a broad high

limited by major NNE-trending listric faults facing the WNW

and cut in the south by the Jan Mayen Fracture Zone (Fig. 1). To

the east, low-angle normal faults are detached between the base

Cretaceous unconformity and a strong seismic marker, which is

structured into tilted blocks and is interpreted as the top base-

ment (Fig. 8e).

Furthermore, Early to mid-Cretaceous (Aptian–Cenomanian?)

normal faulting is observed, concomitant with onlaps, wedging

and erosion features on the eastern flank of the Ran ridge (Fig.

8e). To the west, thinning of the series lying between the base

Cretaceous unconformity and the top basement interval suggests

that the Ran ridge was a depocentre during pre-Cretaceous time.

Its current morphology may result from uplift and inversion of

the pre-Cretaceous depocentre during Early to mid-Cretaceous

time.

During the Late Cretaceous, some faults in the Ran ridge were

reactivated (Fig. 8e). Normal faults associated with the late phase

of rifting are mainly located to the west and do not overprint the

faults belonging to the Ran ridge system. The fault array of the

south Gjallar Ridge cannot be confidently traced into the Ran

basin because of a loose seismic grid and (magmatic) sill

intrusions.

To the NW of the Ran ridge, the Ran basin is a narrow NE-

oriented Cretaceous depocentre severely intruded by sills (Figs 1

and 8e). Several NW-trending transfer zones deduced from

unpublished gravity data affect the Ran basin. This basin is

connected to the north with the small half-graben previously

described in the western limb of the south Gjallar Ridge

(Fig. 8e).

Jurassic to mid-Cretaceous rift events in the outerVøring Basin

The rifting in the outer Vøring Basin has been assigned

previously to a Late Cretaceous–Paleocene episode (Lundin &

Dore 1997; Walker et al. 1997), likely to be Maastrichtian–

Paleocene in age (Ren et al. 1998). In this study, an Early

Campanian age is inferred for the initiation of the late rifting

event. It coincides with a sudden decrease of the sand influx in

the Nyk High and the Vema Dome area, as well with faulting

and uplift in the north Gjallar Ridge, and it is finally linked to a

sudden and major kinematic change in the North Atlantic at

80 Ma, as suggested by Torsvik et al. (2001).

Earlier deformation (mid-Cretaceous and Late Jurassic–ear-

liest Cretaceous?) is also involved in the development of the

outer Vøring Basin. Mid-Cretaceous faulting is observed along

the Ran ridge (Fig. 8e), whereas the axis of the Paleocene rifted

zone is shifted slightly further to the west in the Vøring margin.

Fig. 6. A sand–silicone model of lateral

extension and doming formation (after

Bonini et al. 2001). Lateral flow of a low-

viscosity lower crust (magma chamber),

initially emplaced below the main rift may

have induced uplift of the upper crust and is

accommodated at depth by listric border

faults. This process may explain the

geometry of the Nyk High, which shows

similar structures (Fig. 6a). LC, lower crust;

M, mantle; UC, upper crust.

Fig. 7. Base Tertiary two-way travel time map mixed with a coherence

attribute computed from the 3D seismic survey between the north Gjallar

Ridge and the Gleipne saddle. The north Gjallar Ridge coincides with the

crest of the T reflection mapped at 7.5 s (dashed line). Arrows indicate

fold axes related to Early Eocene inversions. Location of 3D survey is

shown in Figure 1. Late tectonic activity within the Gleipne saddle is

mainly related to minor Early Eocene north–south anticlinal structures in

the eastern part of the survey.

VØRING BASIN, NORWEGIAN HIGH 203

Fig. 8. Seismic line drawing through various segments of the outer Vøring Basin, defined in Table 1. TR, T reflection. Location is shown in Figure 1.

L. GERNIGON ET AL .204

The deep structure of the Ran ridge exhibits low-angle faults

with pre-Cretaceous displacement that could be related to a

Jurassic–earliest Cretaceous rifting controlled by Triassic salt as

documented on the Halten Terrace. Mid-Cretaceous deformation

(mid-Aptian to Cenomanian?) is recorded in the Ran ridge area.

It is considered as a significant rifting phase in the southern

segment and may be correlated with a mid-Cretaceous phase

evidenced in the northern Halten Terrace by Pascoe et al. (1999).

A progressive thinning of the interval between the top base-

ment and the base Cretaceous unconformity to the east in the

Ran ridge suggests that it was a depocentre during pre-Cretac-

eous time (Fig. 8e). Even if the nature of the pre-Cretaceous

series is not well determined, the Ran ridge domains interpreted

as a depocentre during Permian–Late Jurassic(?) was later

uplifted during mid-Cretaceous time synchronously with the

progressive downflexure of the south Vøring Basin. This agrees

with the palaeogeographical interpretations of Brekke et al.

(2001) and Martinius et al. (2001) suggesting an emerged Early–

Mid-Jurassic hinterland located to the east in the current central

Vøring Basin.

Relation between deep and shallow structures

The crustal architecture along the outer Vøring Basin suggests a

direct relationship between the shallow deformation of the basin

and the high-amplitude reflection observed at mid-crustal depth

(Lundin & Dore 1997; Ren et al. 1998). The strike section along

the outer Vøring Basin (Fig. 4) illustrates its mid-crustal

structure, which is mainly characterized by the strong, high-

amplitude T reflection (Gernigon et al. 2001). The T reflection is

clearly mapped from the north Gjallar Ridge to the Ran ridge

whereas it is not observed in the Nyk High on the conventional

seismic data available in this study (Fig. 8).

Mapping of the T reflection reveals three broad high zones,

lying respectively below the north Gjallar Ridge, the south

Gjallar Ridge and the Ran ridge segments (Fig. 10). These mid-

crustal highs strictly correlate with positive gravity anomalies

(Fig. 10). The T reflection exhibits a dome shape with a flat top

at 7.5 s two-way travel time (TWT) beneath the northwestern

part of the north Gjallar Ridge and the Fenris Graben and deeps

below the Vigrid Syncline (Fig. 8). To the south, the T reflection

deepens below the Gleipne saddle, but shallows below the south

Gjallar Ridge (Figs 4, 8 and 10). In this area, the reflection forms

mostly a NW-trending elongated high with two peaks at 7.6 s

TWT, separated by a trough interpreted as a transfer zone that

also affects the shape of the T reflection below the Vigrid

Syncline (Fig. 10). Below the Ran ridge, the underlying T

reflection can be mapped continuously and coincides with the

top basement previously described at 7–8 s TWT (Fig. 10).

However, it shows a morphology characterized by faulted blocks

that differ from the smooth shape observed below the south and

north Gjallar ridges. The faulted blocks occur as NE-oriented

highs, 20–25 km wide, and limited to the south by the Jan

Mayen Fracture Zone and to the north by a NW-trending transfer

zone. The most prominent high corresponds to both the main

Bouguer positive anomaly (Fig. 10) and the highest position of

the Ran ridge at base Cretaceous level.

The geometry of the T reflection is believed to have controlled

the structural evolution of a large part of the outer Vøring Basin.

Cretaceous–Paleocene depocentres preferentially developed

Fig. 9. Depth-converted 3D seismic profile across the north Gjallar Ridge. Rollover structures are controlled at depth by probable (mid?)-Cretaceous

mobile shales (MS). The base Tertiary unconformity truncates a large part of the fault activity. A deep tilted block system is interpreted below the

decollement layer. Between 8 and 12 km, a high-Vp lower-crustal dome is observed, bounded on its top by the T reflection. Seismic depth conversion was

applied using semi-regional seismic interval velocities interpolated with check-shot velocities measured in well 6707/12-1.

VØRING BASIN, NORWEGIAN HIGH 205

where the T reflection is deep, whereas most of the erosional

features at the base Tertiary level occur on the north and south

Gjallar ridge, where the T reflection is shallower (Figs 4 and 8).

Despite uncertainties concerning the Mesozoic picking and

calibration, it is believed that the entire Cretaceous series may be

thinner above the north and south Gjallar ridges compared with

the Gleipne saddle. The domal shape of the T reflection appears

genetically associated with the faulting in the outer Vøring Basin

(Fig. 8) and its structural influence may have started as early as

Campanian–Maastrichtian time. Furthermore, a correlation be-

tween the intensity of intrusions and the geometry of the T

reflection is also inferred from the preferred distribution of sills

in the synform structures overlying the T reflection (Fig. 4).

Implications for the nature of the lower-crustal body ina volcanic margin context

At 7–8 s TWT (10–15 km) below the north and south Gjallar

ridges, the T reflection coincides with the lower-crustal reflection

described by Skogseid & Eldholm (1987), whereas it is shallower

than the Moho estimated by Mjelde et al. (1997) at 20 km depth

below the north Gjallar Ridge. The T reflection coincides with

the top of the lower-crustal body (Vp .7.1 km s�1) determined

by ocean bottom seismometers (OBS) (Mjelde et al. 1997).

Below the Ran ridge, recent OBS data recording shows also that

Vp velocities measured below the T reflection are relatively high,

approximating 6.5–8 km s�1 (T. Raum, personal communica-

tion).

Lundin & Dore (1997) suggested that the dome-shaped T

reflection may represent the top of a lower-crustal diapir,

triggered by mafic underplating, and inducing a fall of viscosity

and a rising of the lower continental crust. This magma-tectonic

process is similar to the model suggested above for the formation

of the Nyk High (Fig. 6). Such a model fits the timing of both

the main magmatic event (commonly dated between 63 and

54 Ma) and the Nyk High uplift (Fig. 5).

In the north Gjallar Ridge, fault patterns above the dome

suggest activity before Paleocene time (Fig. 5). Assuming that

the dome is a magmatic-induced feature (Lundin & Dore 1997)

implies that instantaneous emplacement of thick underplated

bodies had started already during Campanian–Early Maastrich-

tian time in the north Gjallar Ridge domain. However, we are not

aware of any evidence supporting such a young and huge

magmatic activity during this period (e.g. Saunders et al. 1997).

Because the dome strongly influences the structure of the pre-

break-up rifted system in the outer Vøring Basin, the T reflection

is interpreted as probably being a structure emplaced before the

main magmatic event, considered to be Late Paleocene to Early

Eocene in age in the North Atlantic domain (Saunders et al.

1997). From the overall characteristics mentioned above, we

suggest that the crustal dome bounded by the T reflection may be

partly characterized by high-pressure granulite or eclogitic

material that also displays high Vp (7.2–8.5 km s�1) (Fountain et

al. 1994) as documented in the Caledonides of Western Norway

(Austrheim 1990) or below the Mesozoic rifted basins in the

North Sea (Christiansson et al. 2000). This interpretation has

Fig. 10. Time structure map (TWT) of the

T reflection from the north Gjallar Ridge to

the Ran ridge domain. The free air gravity

anomalies fit the shape of the mid-crustal T

reflection.

L. GERNIGON ET AL .206

important implications for thermal history, the mantle tempera-

ture and the magmatic production along the Vøring volcanic

margin because it challenges and minimizes the size of the

Tertiary underplated lower crust, which is generally correlated

with the whole lower-crustal body.

Conclusion

Description of the various segments along the outer Vøring Basin

shows that the Norwegian margin architecture varies along-strike.

Five NE-trending domains, marked by contrasted structural styles

and evolutions, correspond to ridges and sub-basins, named, from

north to south: (1) the Nyk High–Hel Graben; (2) the north

Gjallar Ridge; (3) the Gleipne saddle; (4) the south Gjallar

Ridge; (5) the Ran ridge.

The Ran ridge differs from the other domains as it is a pre-

Cretaceous structure that was subsequently uplifted and affected

by west-verging listric faults during Jurassic?– Early Cretaceous

time. This domain evolved independently with regard to the

Gjallar ridges and Nyk–Hel Graben systems, which were mostly

affected by the Early Campanian–Paleocene rifting leading to

the break-up in Early Eocene time. A strong high-amplitude

reflection at mid-crustal depth is mapped between the north

Gjallar Ridge and the Ran ridge. The so-called T reflection

coincides both with the positive gravity anomalies and the top of

the high-Vp lower-crustal body, previously interpreted as mafic

underplating below the north Gjallar Ridge. A strong correlation

between the shape of the T reflection and the upper-crustal

deformation sealed by Upper Paleocene series suggests that the

lower-crustal body influenced the sedimentary basin before the

break-up and probably started as early as the onset of the latest

rifting in Early Campanian time.

The T reflection is interpreted as the top of a lower-crustal

crystalline body, inferred to be partly Caledonian(?) in age and

displaying an eclogitic nature that may also account for its high

Vp values.

This work was initiated in the framework of the 16th Norwegian

Licensing Round and is part of a PhD thesis at the University of Brest

funded by the TotalFinaElf Exploration Norge Research Centre. This

paper is a contribution to the ‘Sub-Basalt Imaging Project’ involving

TotalFinaElf. The regional interpretation was initiated in 1999 in collab-

oration with the geologists and geophysicists of TotalFinaElf Exploration

Norge in Stavanger and this work has benefited from discussions with

them and their support. We are grateful to C. Ebinger, O.P. Hansen, E.

Lundin, S. Matthews, an anonymous reviewer and the editor A. Maltman

for their constructive criticisms and helpful comments. We thank TGS-

NOPEC, the Norwegian Petroleum Directorate and Norsk Hydro for

permission to publish seismic sections and gravity data.

References

Austrheim, H. 1990. The granulite–eclogite facies transition: a comparison of

experimental work and a natural occurrence in the Bergen Arcs, western

Norway. Lithos, 25, 163–169.

Berggren, W.A., Kent, V., Swisher, C.C. III & Aubry, M.P. 1995. A revised

Cenozoic geochronology and chronostratigraphy. In: Berggren, W.A., Kent,

V., Aubry, M.P. & Hardenbol, J. (eds) Geochronology, Times Scales and

Global Stratigraphic Correlation. Society for Sedimentary Geology, Special

Publications, 54, 129–212.

Berndt, C., Skogly, O.P., Planke, S., Eldholm, O. & Mjelde, R. 2000. High

velocity break-up related sills in the Vøring Basin off Norway. Journal of

Geophysical Research, 105(B12), 28443–28455.

Berndt, C., Planke, S., Alvestad, E., Tsikalas, F. & Rasmussen, T. 2001.

Seismic volcanostratigraphy of the Norwegian margin: constraints on tectono-

magmatic break-up processes. Journal of the Geological Society, London,

158, 413–426.

Bjørnseth, H.M., Grant, S.M., Hansen, E.K., Hossack, J.R., Roberts, D.G. &

Thompson, M. 1997. Structural evolution of the Vøring Basin, Norway,

during the Late Cretaceous and Paleogene. Journal of the Geological Society,

London, 154, 559–563.

Blystad, P., Brekke, H., Faerseth, R.B., Larsen, B.T., Skogseid, J. &

Tørudbakken, B. 1995. Structural Elements of the Norwegian Continental

Shelf, Part II. The Norwegian Sea Region. Norwegian Petroleum Directorate

Bulletin, 8.

Bonini, M., Sokoutis, D., Mulugeta, G., Boccaletti, M., Corti, G.,

Innocenti, F., Manetti, P. & Mazzarini, F. 2001. Dynamics of magma

emplacement in centrifuge models of continental extension with implications

for flank volcanism. Tectonics, 20(6), 1053–1065.

Brekke, H. et al.2000. The tectonic evolution of the Norwegian Sea continental

margin with emphasis on the Vøring and Møre Basins. In: Nøttvedt, A.

(ed.) Dynamics of the Norwegian Margin. Geological Society, London,

Special Publications, 167, 327–378.

Brekke, H., Sjulstad, H.I., Magnus, C. & Williams, R.W. 2001. Sedimentary

environments offshore Norway—an overview. In: Martinsen, O. & Dreyer,

T. (eds) Sedimentary Environments Offshore Norway—Palaeozoic to Recent.

Norsk Petroleums Forening, Special Publications, 10, 1–5.

Christiansson, P., Faleide, J.I. & Berge, A.M. et al.2000. Crustal structure in

the northern North Sea: an integrated geophysical study. In: Nøttvedt, A.

(ed.) Dynamics of the Norwegian Margin. Geological Society, London,

Special Publications, 167, 15–40.

Dam, G., Larsen, M. & Sønderholm, M. 1998. Sedimentary response to mantle

plumes: implications from Paleocene onshore successions, West and East

Greenland. Geology, 26, 207–210.

Dore, A.G., Lundin, E.R., Jensen, L.N., Birkeland, Ø., Eliassen, P.E. &

Fichler, C. 1999. Principal tectonic events in the Northwest European

Atlantic margin. In: Fleet, A.J. & Boldy, S.A. (eds) Petroleum Geology of

Northwest Europe: Proceedings of the 5th Conference. Geological Society,

London, 41–61.

Eldholm, O. & Grue, K. 1994. North Atlantic volcanic margins: dimensions and

production rates. Journal of Geophysical Research, 99, 2955–2968.

Eldholm, O., Thiede, J. & Taylor, E. 1989. Evolution of the Vøring volcanic

margin. In: Eldholm, O., Thiede, J. & Taylor, E. (eds) Proceedings of the

Ocean Drilling Program, Scientific Results. Ocean Drilling Program, College

Station, TX, 104, 1033–1065.

Eldholm, O., Gladczenko, T.P., Skogseid, J. & Planke, S. et al.2000. Atlantic

volcanic margins: a comparative study. In: Nøttvedt, A. (ed.) Dynamics of

the Norwegian Margin. Geological Society, London, Special Publications,

167, 411–428.

Fountain, D.M., Boundy, T.M., Austrheim, H. & Rey, P. 1994. Eclogite-facies

shear zones—deep crustal reflectors? Tectonophysics, 232, 411–424.

Geoffroy, L., Gelard, J.P., Aite, R. & Cattaneo, G. 2001. Comments on ‘New

insight into the structure of the Nuussuaq Basin, central West Greenland

[from Chalmers, Pulvertaft, Marcussen and Pedersen, Marine and Petroleum

Geology, 1999, 16, 197–234]’. Marine and Petroleum Geology, 18, 947–952.

Gernigon, L., Ringenbach, J.C., Planke, S., Jonquet-Kolstø, H. & Le Gall,

B. 2001. Segmentation of rifting and magmatism along the Outer Vøring

Basin, Mid-Norway margin. In: American Association of Petroleum Geolo-

gists, Annual Meeting 2001, Extended Abstracts. CDRom.

Hjelstuen, B.O., Eldholm, O. & Skogseid, J. 1999. Cenozoic evolution of the

northern Vøring margin. Geological Society of America Bulletin, 111(12),

1792–1807.

Kittilsen, J.E., Olsen, R.R., Marten, R.F., Hansen, E.K. & Hollingsworth,

R.R. 1999. The first deepwater well in Norway and its implications for the

Upper Cretaceous Play, Vøring Basin. In: Fleet, A.J. & Boldy, S.A.R. (eds)

Petroleum Geology of Northwest Europe: Proceedings of the 5th Conference.

Geological Society, London, 276–280.

Koch, J.O. & Heum, O.R. 1995. Exploration trends of the Halten Terrace. In:

Hanslien, S. (ed.) Petroleum Exploration and Exploitation in Norway. Norsk

Petroleums Forening, Special Publications, 4, 235–251.

Lundin, E.R. & Dore, A.G. 1997. A tectonic model for the Norwegian passive

margin with implications for the NE Atlantic: Early Cretaceous to break-up.

Journal of the Geological Society, London, 154, 545–550.

Lundin, E.R. & Dore, A.G. 2002. Mid-Cenozoic post-breakup deformation in the

‘passive’ margins bordering the Norwegian–Greenland Sea. Marine and

Petroleum Geology, 19, 79–93.

Lundin, E.R., Rønning, K., Dore, A.G. & Olesen, O. 2002. Hel Graben, Vøring

Basin, Norway—a possible major cauldron? 25th Nordic Geological Winter

Meeting, 6–9 January, Reykjavik, Abstract Volume. 132.

Martinius, A.W., Kaas, I., Næss, A., Helgesen, G., Kjærefjord, J.M. & Leith,

D.A. 2001. Sedimentology of the heterolithic and tide-dominated Tilje

formation (Early Jurassic, Halten Terrace, offshore mid-Norway). In:

Martinsen, O. & Dreyer, T. (eds) Sedimentary Environments Offshore

Norway—Palaeozoic to Recent. Norsk Petroleums Forening, Special Publica-

tions, 10, 103–144.

VØRING BASIN, NORWEGIAN HIGH 207

Mjelde, R., Kodaira, S., Shimamura, H., Kanazawa, T., Shiobara, H., Berg,

E.W & Riise, O. 1997. Crustal structure of the central part of the Vøring

Basin, mid-Norway margin from ocean bottom seismographs. Tectonophysics,

277, 235–257.

Mogensen, T.E., Nyby, R., Karpuz, R. & Haremo, P. et al.2000. Late Cretaceous

and Tertiary structural evolution of the northeastern part of the Vøring Basin,

Norwegian Sea. In: Nøttvedt, A. (ed.) Dynamics of the Norwegian Margin.

Geological Society, London, Special Publications, 167, 379–396.

Mutter, J.C., Talwani, M. & Stoffa, P.L. 1984. Evidence for a thick oceanic

crust off Norway. Journal of Geophysical Research, 89, 483–502.

Pascoe, R., Hooper, R., Storhaug, K. & Harper, H. 1999. Evolution of

extensional styles at the southern termination of the Nordland Ridge, Mid-

Norway: a response to variations in coupling above Triassic salt. In: Fleet,

A.J. & Boldy, S.A.R. (eds) Petroleum Geology of Northwest Europe:

Proceedings of the 5th Conference. Geological Society, London, 83–90.

Planke, S., Skogseid, J. & Eldholm, O. 1991. Crustal structure off Norway, 628

to 708 north. Tectonophysics, 189, 91–107.

Ren, S., Skogseid, J. & Eldholm, O. 1998. Late Cretaceous–Paleocene extension

on the Vøring volcanic margin. Marine Geophysical Research, 20, 343–369.

Robert, A.M., Lundin, E.R. & Kuznir, N.J. 1997. Subsidence of the Vøring

Basin and the influence of the Atlantic continental margin. Journal of the

Geological Society, London, 154, 551–557.

Sandwell, D.T. & Smith, W.H.F. 1997. Marine gravity anomaly from Geosat

and ERS1 satellite altimetry. Journal of Geophysical Research, 102(B5),

10039–10054.

Saunders, A.D., Fitton, J.G., Kerr, A.C., Norry, M.J. & Kent, R.W. 1997. The

North Atlantic Igneous Provinces. In: Mahoney, J.J. & Coffin, M.F. (eds)

Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcan-

ism. American Geophysical Union, Geophysical Monograph, 100, 45–93.

Skogseid, J. 1994. Dimensions of the Late Cretaceous–Palaeocene Northeast

Atlantic rift derived from Cenozoic subsidence. Tectonophysics, 240,

225–247.

Skogseid, J. & Eldholm, O. 1987. Early Cenozoic crust at the Norwegian

continental margin and the conjugate Jan Mayen Ridge. Journal of

Geophysical Research, 92(B11), 11471–11491.

Skogsied, J. & Eldholm, O. 1989. Vøring plateau continental margin: seismic

interpretation, stratigraphy and vertical movements. In: Eldholm, O.,

Thiede, J. & Taylor, E. (eds) Proceedings of the Ocean Drilling Program,

Scientific Results. Ocean Drilling Program, College Station, TX, 104,

993–1030.

Skogseid, J., Pedersen, T., Eldholm, O. & Larsen, B.T. 1992. Tectonism and

magmatism during NE Atlantic continental break-up: the Vøring basin. In:

Storey, B.C., Alabaster, T. & Pankhurst, R.J. (eds) Magmatism and the

Causes of Continental Break-up. Geological Society, London, Special

Publications, 68, 305–320.

Skogseid, J., Planke, S., Faleide, J., Pedersen, T., Eldholm, O. & Neverdal,

F. et al.2000. NE Atlantic continental rifting and volcanic margin formation.

In: Nøttvedt, A. (ed.) Dynamics of the Norwegian Margin. Geological

Society, London, Special Publications, 167, 295–326.

Swieciki, T., Gibbs, P.B., Farrow, G.E. & Coward, M.P. 1998. A tectonostrati-

graphic framework for the Mid-Norway region. Marine and Petroleum

Geology, 15, 245–276.

Torsvik, T.H., Mosar, J. & Eide, E. 2001. Cretaceous–Tertiary geodynamics: a

North Atlantic exercise. Geophysical Journal International, 146, 850–866.

Tsikalas, F., Faleide, J.I. & Eldholm, O. 2001. Lateral variations in tectono-

magmatic style along the Lofoten–Vesteralen volcanic margin off Norway.

Marine and Petroleum Geology, 18, 807–832.

Walker, I.M., Berry, K.A., Bruce, J.R., Bystøl, L. & Snow, J.H. 1997.

Structural modelling of regional depth profiles in the Vøring Basin:

implications for the structural and stratigraphic development of the Norwe-

gian passive margin. Journal of the Geological Society, London, 154,

537–544.

White, R.S. & McKenzie, D. 1989. The generation of volcanic continental

margins and flood basalts. Journal of Geophysical Research, 94, 7685–7729.

Received 22 April 2002; revised typescript accepted 7 November 2002.

Scientific editing by Alex Maltman

L. GERNIGON ET AL .208