Tectonophysics 231(1994) 71-84
Stratigraphy, tectonostratigraphy and the accretion of outboard
terranes in the Caledonides of Sunnhordland, W. Norway
T.B. Andersen
*, A. Andresen
Institutt for Geologi, Universitetet i Oslo, P.O. Box 1047, 0316 Blindem, Oslo 3, Norway
(Received May 11,1992; revised version accepted November 14,1992)
Abstract
The Caledonides
between Karmoy and Bergen in western Norway represent one of the best studied sections of
the Scandinavian Caledonides, and the area is of particular significance with regard to the geological evolution of the
Caledonian outboard terranes. These terranes include ophiolites of Early Ordovician age, immature to mature
island-arc and arc-basin lithologies of Early to Middle Ordovician age and Late Ordovician to Early Silurian
unconformable transgressive and regressive sequences. The stratigraphy, including several unconformities, as well as
the tectonothermal evolution of this composite terrane, demonstrate that the assembly of the terrane was associated
with deformation, metamorphism and syntectonic emplacement of arc plutons prior to the Scandian continental
collision between Baltica and Laurentia. The evidence for the pre-Scandian deformation of these rocks has
previously been used as an argument for the accretion of oceanic rocks to Baltica prior to the Scandian orogeny. We
dispute this interpretation and conclude that the early Caledonian deformation or this terrane occurred within the
Iapetus Ocean.
1. Introduction
The Caledonides in the coastal region south of
Bergen (Fig. 1) have attracted considerable interest since the classical study of Reusch (1888).
Reusch discovered and described most of the
rare and important fossil localities of the region.
A step forward in the understanding of the Scandinavian Caledonides came when major parts of
the mafic igneous complexes of western Norway
were recognised as ophiolite/ island-arc complexes; first on the island of Karmoy (Sturt and
* Corresponding author.
Thon, 1978a). The work on the ophiolites and
their cover sequences in the late seventies and
early eighties resulted in several tectonic interpretations, concluding that ophiolitic terranes
were accreted to Baltica in the Early Ordovician
(Brekke et al., 1984; Sturt, 1984; Sturt et al.,
1985). The initial studies on the ophiolites were
succeeded by a comprehensive mapping programme, combined with detailed geochemical and
petrological studies, by staff and students from
the University of Bergen. An important conclusion of these studies was that the ophiolites of the
region were formed in subduction-related
palaeoenvironments (Pedersen et al., 1988). U/Pb
dating on some of these complexes, carried out by
0040-1951/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved
SSDI 0040-1951(93)E0116-C
72
T. B. Andersen, A. Andresen / Tectonophysics 231 (1994) 71-84
Pedersen and co-workers (Dunning and Pedersen, 1988; Pedersen et al., 1988; Pedersen and
Dunning, in prep.), together with the geological
and paleontological data from the region, have
enabled a much better understanding and timing
of the processes that occurred within the outboard terranes prior to their accretion to Baltica
during the Scandian orogeny (Andersen et al.,
1990; Pedersen et al., 1992). Because of the similarity in age and origin of ophiolitic complexes in
Scandinavia and Newfoundland, it has recently
been suggested that Scandinavian ophiolite complexes of Early to Middle Ordovician age (“Group
1”) were accreted to Laurentia during the Ordovician “Taconic orogeny” (Dunning and Pedersen, 1988; Pedersen and Furnes, 1991; Pedersen
et al., 1991; Pedersen and Dunning, in prep.1 and
that they were rifted away from Laurentia by
back-arc spreading and emplaced onto Baltica
during the Scandian continental collision between
Baltica and Laurentia.
The tectonostratigraphic
succession between
Karmoy and Bjarnatjorden in western Norway
(Fig. 2) is the product of polyphase Caledonian
shortening events, and the subsequent extensional collapse of the orogen. This paper gives an
overview of the tectonostratigraphy of the southwest Norwegian Caledonides, and discusses the
tectonostratigraphy
in the light of the terrane
models into which the nappe stack of the Scandinavian Caledonides normally is fitted (Dallmeyer
and Gee, 1986; Roberts, 1988; Stephens and Gee,
1989). It further summarises the internal stratigraphic relationships of the southwest Norwegian
outboard terranes and provides the basis for discussing the accretional history of the Caledonian
outboard terranes in the coastal region south of
Bergen (Fig. 11.
pJ
PERMIAN
DEVONIAN
(UPPERMOST ALDCHTHOh’
NOT PRESi%T INS.NORWAY)
UPPER ALLOCHTHON
lissi
EXOTIC PRKAMBRLM
CRUST & COVER
MlDDLE ALLOCHTHON
m
mLnc-aCom
LOWER ALLOCHTHON
PARAUTOCHTHON
& AUTOCHTHON
Fig. 1. Schematic tectonostratigraphic map of southern Norway. The Jotun Nappe and its lateral equivalents along the west coast
have speculatively been assigned to the Upper Allochthon as they apparently are structurally underlain by eugeoclinal rocks.
T.B. Andersen, A. Andresen / Tectonophysics 231 (1994) 71-84
1.1. Tectonostratigraphy
The tectonostratigraphy
of the Scandinavian
Caledonides is normally divided into the follow-
13
ing five main units as summarised by Roberts and
Gee (1985):
(1) The Autochthon-Parautochthon
comprises the basement of the Fennoscandian Shield
SIMPLIFIED GEOLOGICAL MAP OF THE
SUNNHORDLAND REGION, W. NORWAY
BJQRNAFJORDEN
GRANODIORITE
UNCONFORMABLE UP. ORDOVICIAN
- LR. SILURI~
SKUDESNES, VKAFJORD,
DYVIKVAGEN.
OS GPS..
GI&NLW?d
I VOLCANIC COVER ON
OPmOLlTR. / .iRC COMPLEXES: TORVASTAD.
DEEP-MARINE
LANGEVAG
, MUNDHI3A
ARC - VOLCANICS
SIGGJO & KAlTNAKKEN
GPS
&SEDIMENTS,
GF’S
Fig. 2. Simplified geological map of the outer Hardanger-Sunnhordland
and tectonostratigraphic units discussed in the text.
ca 475 Ma
HUGL.O & SKJELNE3
FM
area, showing the distribution of the main stratigraphic
74
T B. A&men, A. Andresen / Tectonophysics 231 (I 994) 71-84
and the cover of late Proterozoic and early
Palaeozoic age.
(2) The Lower Allochthon consists mainly of
low-grade sedimentary sequences of late Proterozoic to early Palaeozoic age. In the upper parts of
the Lower Allochthon, basement lithologies of
the Fennoscandian Shield are involved in the
thrust sheets.
(3) The Middle Allochthon is dominated by
Precambrian gneiss complexes and thick psammitic sequences, which locally are overlain by
Vendian to lower Palaeozoic metasediments.
(41 The Upper Allochthon contains the early
Palaeozoic outboard terranes, including ophiolites and island-arc complexes. The Lower to
Middle Ordovician fossiliferous assemblages in
the upper part of this unit contain a Laurentian
Toquima-Table
Head fauna clearly showing its
exotic relationship to Baltica (Bruton and Bockelie, 1980; Pedersen et al., 1992). The lower parts
of the Upper Allochthon (the Seve Nappes and
their lateral equivalents), however, also contain
Precambrian gneisses, schists, amphibolites and
eclogitised mafic volcanics, parts of which are
believed to have constituted transitional continental-oceanic crust segments of the rifted margin of Baltica (Dallmeyer and Gee 1986; Mark et
al., 1988; Stephens and Gee, 1989; Dallmeyer et
al., 1991).
(5) The Uppermost Allochthon is present only
in Nordland and Troms. This unit comprises a
heterogeneous complex of nappes, dominated by
schists, marbles, granitoids and gneisses. It also
contains ophiolitic and other ensimatic lithological associations in the Helgeland Nappe Complex. In the Tromso Nappe, the highly sheared
schists and gneisses also include mafic pods with
well-preserved Caledonian eclogite facies rocks
(Krogh et al., 1990).
1.2. Tectonosta tigrfphy and terrane analysis
In terrane analysis, the tectonostratigraphic
units 1 to 3 as well as the lowermost part of unit 4
are considered to represent Baltic crust, platform, miogeocline and transitional continentaloceanic crust, respectively (Roberts, 1988; Stephens and Gee, 1989). The remaining parts of the
Upper Allochthon are considered to form the
vestiges of the Iapetus Ocean, while the Uppermost Allochthon represents a composite oceanic-continental
terrane, for which a definite
evolutionary history and origin is still very uncertain; a Laurentian origin has been suggested for
the Uppermost Allochthon (Sturt et al., 1984;
Dallmeyer and Gee, 1986; Stephens and Gee,
1989). In the Hardanger-Sunnhordland
region,
units 1 to 4 are present (Figs. 1 and 2). This
tectonostratigraphy represents the main basis for
the various terrane models, last summarised by
Stephens and Gee (1989), for the Scandinavian
Caledonides. In these models, the exotic, composite oceanic terranes have been taken to define
one major level in the tectonostratigraphy
that
consequently may be regarded as a major complex suture zone across which the Iapetus Ocean
was closed during the Scandian continental collision between Baltica and Laurentia.
In southern Norway, the interpretation of a
single major suture zone must be regarded with
some caution. Although poorly preserved, ophiolitic and other oceanic rock complexes occur
structurally beneath the Jotun and other continental crystalline nappes that are commonly assigned to the Middle Allochthon as an imbricated
part of Baltica (Roberts, 1988; Stephens and Gee,
1989). The occurrences of oceanic lithologies, including large massifs of gabbros, amphibolites
and serpentinised hartzburgites as well as mafic
volcanites at low structural levels beneath the
crystalline continental crust of the Jotun Nappe
along its northwestern margin Wgmond et al.,
1984; Pedersen et al., 19881, and under the
Jotun-kindred rocks of the Dalsfjord Suite in
Sunnfjord (Fumes et al., 1976; Swensson and
Andersen, 1990, indicate that rocks normally interpreted as oceanic are present structurally beneath and above the continental crystalline massifs (Fig. 1). Similarly, the dismembered Vlg%mo
Ophiolite near Otta in central southern Norway
(Sturt et al., 1991) apparently occupies an enigmatic tectonostratigraphic
position with respect
to the Jotun Nappe. On the other hand, the
unconformable relationships between the Jotun
gneisses and “sparagmites” in the Valdres area
(Milnes and Koestler, 19851, and along the north-
75
T.B. Andersen, A. Andresen / Tectonophysics 231 (1994) 71-84
western side of the Jotun
support a more traditional
Precambrian rocks of the
formed part of the Baltic
synform (Lutro, 1988)
interpretation that the
Jotun Nappe originally
Shield basement.
2. The Sunnhordland region
2.1. The Autochthon, Lower Allochthon and the
status of the Mddle Allochthon in central southern
Norway
The Hardangervidda section (Figs. 1 and 3)
preserves the autochthonous Precambrian basement and a thin autochthonous to parautochthonous fossiliferous cover of Cambrian to Ordovician (Llanvimian) age (Andresen, 1978,1982;
Andresen and Faerseth, 1982). The autochthon
and parautochthon
are structurally overlain by
the allochthonous Holmasjo-Valen
mica schists
of assumed early Palaeozoic age, and the Precam-
brian continental
crystalline massifs of the
Hardanger-Ryfylke
and Halsnoy Nappe complexes (Solli et al., 1978). In most of the recent
geotectonic reconstructions, these units have been
assigned to the Baltic continental margin and
constitute the Lower and Middle allochthons in
the area (Roberts and Gee, 1985; Stephens and
Gee, 1989; and others). As indicated above, the
interpretation (Roberts and Gee, 1985; Stephens
and Gee, 1989) of the Precambrian nappes on
Hardangervidda
as part of the original Baltic
craton is questionable because they are underlain
by spatially restricted but nevertheless important
volcanites and volcaniclastics that occur on central Hardangervidda (Fig. 3) (Andresen, 1982).
On central Hardangervidda, the undated pillow basalts and green tuffaceous sediments of
talc-alkaline affinity (Andresen, 1982) are found
in contact with the platform sediments (Cambrian
to Llanvimian) that constitute the parautoch-
TECTONOSTRATIGRAPHY I STRATIGRAPHIC RELATIONSHIPS. SUNNHO~~~,
1111
B0hlL0-
STORD
HUGLO - 0LVE - VARALDS0Y
SOUTHERN STORD
w. NORb’AY
SE OF
EARDANGERFJORDEN
SE
7
z
z
Fig. 3. A compilation of the tectonostratigraphy
eugeoclinal, outboard terranes.
and stratigraphy in the Caledonides of southwestern Norway, with emphasis on the
76
T.B. Andersen. A. Andresen / Tectonophysics
thonous cover (Lower Allochthon) to the Baltic
basement (Andresen, 1974, 1978, 1982). The
tectonostratigraphic
position of these mafic volcanites is clearly beneath
the Precambrian
Hardanger-Ryfylke
and Jotun Nappe complexes
(Figs. 2 and 3). In the Sunnfjord area, gabbros
and greenschists occur structurally below the
Dalsljord Suite, within the mylonites of the
Kvamshesten detachment (Swensson and Andersen, 1991). The Dalsfjord Suite is lithologically
and tectonostratigraphically
correlated with the
Jotun Nappe (Sigmond et al., 1984). It may,
therefore, be suggested that suture zones occur
both above and beneath the Jotun Nappe and its
lateral equivalents of the Middle Allochthon in
southern Norway. These fragments of Precambrian continental crust may represent a microcontinent that, at least in parts, was separated
from Baltica, presently expressed by the highly
deformed and attenuated oceanic rocks that are
exposed intermittently along their basal tectonic
contacts. Consequently these parts of the Middle
Allochthon in southern Norway may be regarded
as “suspect” with respect to the Fennoscandian
Shield (Andersen et al., 1991a,b; Pedersen et al.,
1988, 1992). An alternative explanation may be
that the ophiolitic and subduction-related
volcanic rocks that occur structurally beneath the
Jotun Nappe are related to large-scale out-of-sequence thrusts, or late and very large scale overturned folds of the tectonostratigraphy,
which
included the already abducted oceanic terranes
of the Upper Allochthon. More detailed structural studies, combined with accurate dating of
the “oceanic-type”
lithologies that are sandwiched between the Jotun Nappe and the allochthonous Baltic basement are required before
firm conclusions concerning the status of the Jotun Nappe are reached.
The nappe complexes on Hardangervidda are
structurally separated from the overlying undisputed outboard sequences of the Upper Allochthon by a.major thrust zone. The thrust zone
has been reactivated in a large-scale extensional
fold and fault system, that strikes northeastsouthwest, parallel with Hardangerfjorden
(Figs.
2 and 3). This large-scale composite extensional
structure was identified and originally described
231 (1994) 71-84
as the “Faltungsgraben” (Figs. 2 and 3) by GoldSchmidt (1912). Throughout Hardangervidda the
shortening structures and the generally flat-lying
nappe boundaries have been modified variably by
“back-folding”
and late W-vergent structures
(Andresen, 1982). As far east as the Haukelidseter area on south-central Hardangervidda (Fig.
0, a pronounced extensional crenulation cleavage demonstrates that a considerable re-activation can be assigned to the extensional collapse of
the orogen. Reconnaissance
studies along the
southeastern margin of the Jotun Nappe show
that the underlying rocks in places are characterised by penetrative,
top-to-the-west,
extensional fabrics, which may account for the restricted occurrences of oceanic lithologies along
this nappe boundary. Fabrics related to the extension are intense and locally mylonitic along
the southeastern coast of Hardangerfjorden such
as in the Tittelsnes area on northern Haugalandet (Fig. 2). The offshore expression of the
“Faltungsgraben”
has been imaged in deepseismic reflection profiles (Hurich and Kristoffersen, 1988) as a strong, NW-dipping reflector to
the base of the crust that offsets the present
Moho reflectors.
On the northwestern side of the Faltungsgraben, basement and cover are overlain by highly
attenuated allochthonous Precambrian rocks (Fig.
31, preserved immediately to the north of the
area shown in Fig. 2 (Naterstad and Jorde, 1981;
Ragnhildstveit, 1987). Little published structural
data are available from these rocks, but J. Naterstad (pers. commun.) considers the lower units
(Fig. 3) to represent the westward continuation of
the Lower and Middle allochthonous rocks southeast of the “Faltungsgraben”.
2.2. The Upper Allochthon
The geological evolution of the oceanic terranes of the Upper Allochthon in western Norway is relatively well known. This is one of the
key areas from which to unravel the geological
evolution of the Iapetus Ocean from the Early
Ordovician onwards in the Caledonides (Pedersen et al., 1988, 1992).
T.B. A&men, A. Andresen / Tectonophysics231 (1994) 71-84
2.3. Bgmlo and Stord
Of particular importance are the islands of
Bomlo, Stord and Karmoy (Figs. 1 and 21, where
fossils, precise U-Pb zircon ages (Dunning and
Pedersen, 1988; Pedersen and Dunning, in prep.)
and detailed studies of the field relationships
enable refinement and revision of previous models. The geology of Karmoy has been presented in
several studies (Sturt and Thon, 1978a,b; Thon,
1980; Pedersen and Hertogen, 1990) and most
recently by Pedersen and Dunning (in prep.). The
intrusive and stratigraphic relationships of Bornlo
and Stord are summarised in Fig. 3 and by Andersen et al. (1991b).
Geochemical studies demonstrate that the formation of the ophiolitic rocks was related to the
initiation of ensimatic plate convergence, as all
the ophiolites originated in an arc/ back-arc environment. The evolution records a long period
( N 495-470 Ma) when these complexes resided in
an oceanic supra-subduction zone setting (Pedersen et al., 1988). With time, this produced a
mature magmatic arc, but it is not clear whether
it included continental crust. (Andersen and
Jansen, 1987; Pedersen et al., 1988; Andersen et
al., 1991b). Formation of the arc was associated
with local intense deformation during emplacement of various plutons (Andersen, 1989; Andersen et al., 1991b). The regional inversion of the
Lykling-Geitung
ophiolite/ arc complex on
Bomlo described by NordHs et al. (19851, occurred prior to the deposition of the Siggjo and
Kattnakken volcanites (476-473 Ma) and the intrusion of the talc-alkaline Vardafjellet Gabbro
at 472 f 2 Ma (Pedersen and Dunning, 1991).
This interpretation is at variance with previous
interpretations (Brekke et al., 1984; Sturt et al.,
1984; Sturt, 1984; Furnes et al., 19851, who argued that the early deformation of the ophiolites
occurred during accretion to Baltica in an early
Caledonian, Finnmarkian event. The U-Pb ages
(Pedersen and Dunning, 1991, in prep.) from the
S-type granites of the West Karmoy Igneous
Complex (WKIC) (N 475 Ma) intruding the
Karmoy Ophiolite, and the Siggjo and Kattnakken volcanites with continentally influenced
geochemistry, are still enigmatic (Brekke et al.,
17
1984; Nordls et al., 1985). Pedersen et al. (1988)
suggested that the ophiolitic rocks were accreted
to Laurentia
during the Middle Ordovician
Taconic event. More recently, however, Pedersen
and Dunning (1991) suggested that the continental signature could be a result of partial melting
and contamination of subducted, continentally
derived sediments and that this probably occurred in an intra-oceanic setting. U/Pb dating
of zircons from WKIC demonstrates that the
provenance of these rocks was an old, Archaean
crust, unlike the exposed southern parts of the
Baltic Shield, as there is a massive inheritance of
zircons with cores of this age (Pedersen and Dunning, 1991, in prep.).
Of particular importance and significance in
the eugeoclinal terranes of southwestern Norway
are the stratigraphic discontinuities, including angular unconformities, non-conformities and disconformities that have been identified (Foslie,
1955; Sturt and Thon, 1976, 1978b; Naterstad,
1976; Thon, 1980, 1985; Thon et al., 1980; Andersen et al., 1984; Brekke et al., 1984; Nordis et al.,
1985; Andersen et al., 1991b). The unconformities stratigraphically below the Middle to Upper
Ordovician and Lower Silurian rocks were suggested previously to represent a major stratigraphic hiatus following early Caledonian, Finnmarkian abduction of “Group I” ophiolites onto
Baltica (Fumes et al., 1985). The unconformity
on the ‘Group 1’ ophiolites was considered to be
traceable along the Scandinavian Caledonides
from Lyngen in Troms, northern Norway to
Karrnoy (Sturt, 1984; Sturt et al., 1985; Thon,
1985).
In southwestern Norway, the pre-Ashgillian
Siggjo and Kattnakken (Bgmlo and Stord, Figs. 2
and 3) volcanites are unconformable on the Lykling-Geitung ophiolite/ arc complex (Nord;Ps et
al., 1985). The stratigraphic relationships on
Born10 and Stord, with Middle Ordovician volcanites (476-473 Ma) overlain by Ashgillian sediments, suggested that the early Caledonian orogenie event affecting the ophiolite and arc
lithologies was of Early Ordovician age and
broadly coeval with the Finnmarkian phase as
originally defined in its type area (Sturt et al.,
1978; Sturt 1984). An important problem in as-
78
T.B. Andersen, A. Andresen / Tectonqhysics
signing the pre-Scandian deformation
of the
ophiolitic rocks to a major phase of abduction
onto a continent at this time is the apparent lack
of (1) continental, terrane-linking detritus in the
unconformable sequences, (2) stitching plutons or
(3) observations of terrane-linking, overstepping
unconformable contacts in western Norway.
Recently, Sturt et al. (19911, argued that the
V&g&m0 ophiolite underlying the ArenigianLlanvimian serpentinite conglomerates of the Se1
Group in the Otta area (Fig. 1) of central southern Norway was abducted onto the margin of
Baltica prior to the deposition of the fossiliferous
Lower-Middle Ordovician serpentinite conglomerates. They suggested that the stratigraphic relationships between the Late Precambrian (?> Heida1 series, the Vig%mo ophiolite and the unconformable Arenigian-Llanvirnian
Se1 Group show
that the ophiolite was abducted onto the Heidal
series prior to the deposition of the Se1 Group.
The Heidal series rocks are traditionally correlated with the Vendian “sparagmites” of Baltica
(Strand, 1951, 1964). The evidence that is presented in support of their tectonic model is discussed below, and alternative interpretations for
major abduction-related
deformation invoked by
Sturt et al. (1991) may be suggested to explain the
ultramafic-dominated
Arenigian-Llanvirnian
conglomerates described from the Se1 Group.
2.4. Varalds@y
Until recently, the stratigraphic relationships
on the island of Varaldsoy in the central parts of
Hardangerfjorden
(Figs. 2 and 3) have not been
studied since Foslie’s impressive mapping in the
forties, published post-mortem;
Foslie (1955,
edited by Dietrichson). Although not specifically
stated in this paper, Foslie’s map and petrographic descriptions clearly indicate the presence
of two major stratigraphic discontinuities on the
island, and this has been supported by recent
mapping by the present authors and two students
(Mseland, pers. commun.; Ado&en, pers. commun.). The Varalds(sy-0lve Complex (Figs. 2 and
3) comprises undated ophiolitic and island-arc
lithologies including talc schists, a high-level gabbra/ sheeted dyke complex, intrusive quartx-di-
231 (1994) 71-84
orites, pillow lavas/volcaniclastics,
partly with an
andesitic composition (Faerseth, 1982), and a sequence of rhyolitic metavolcanites in the Sl$.lnes
area (Fig. 2). The silicic metavolcanites are overlain by limestones in which poorly preserved
crinoid fragments occur at several localities (observations by the present authors and co-workers).
The limestones are overlain by a thick sequence
of dark phyllites which locally contains coticules.
Conglomerates with pebbles from the stratigraphically underlying rhyolitic rocks occur at the base
of the marbles at Varaldscby, in the Olve area and
on Huglo (Faerseth, 19821, suggesting a disconformable contact at this level; however, no structural or metamorphic break has been identified
between
the 0lve-Varaldsoy
Complex, the
Skjelnes-Huglo metavolcanites and the overlying
limestones and marbles.
On northern Varaldsoy, however, the 0lveVaraldsay Complex is non-conformably overlain
by the Mundheim Group (Figs. 2 and 3). The
basal conglomerates of the Mundheim Group
contain elastic material derived from various parts
of the (alve-Varaldsoy
Complex (Foslie, 1955;
Maeland, pers. commun.), indicating that the contact represents a major hiatus with deep erosion
of the ophiolite/arc
lithologies. The basal conglomerates are succeeded by pebbly and albiterich arkoses, limestones with poorly preserved
crinoid fragments, and a thick sequence of deepmarine phyllites, cherts and metagreywackes with
greenstone detritus (Foslie, 1955). The provenance for the sedimentary rocks in the Mundheim Group is dominated by the underlying
oceanic lithologies. In this respect, the Mundheim Group is similar to the rocks unconformable on the Tgrvikbygd ophiolite fragment
further to the northeast along Hardangerfjorden
(Andersen et al., 1984). Southwestwards, in the
eastern Tysnesay area (Fig. 21, laterally equivalent rocks of the Mundheim Group also contain
basaltic metavolcanites (Rundhovde, 1987). The
Mundheim Group is mappable almost continuously along strike to Bramlo, where Brekke (19831
used the name Lange&g Group for these rocks.
The age of the Mundheim-Lang&g
groups is
unknown, but its lithostratigraphy, particularly the
thick development
of deep-marine
phyllites,
T. B. Andersen,
A. Andresen
cherts and greywackes, makes a correlation with
the Late Ordovician-Early
Silurian shallowmarine, transgressive sequences (see below) in
western Norway unlikely. It is tentatively proposed that the Mundheim-Langevig
groups may
represent a Middle Ordovician arc-basin sequence more akin to the Torvastad Group on
Karmoy (see below, Figs. 2 and 3).
The unconformable
Gr&nut Formation on
Varaldsoy (Figs. 2 and 3) was first mapped by
Foslie (19551, and is preserved in a tight syncline
on the central part of the island. The metasediments in this formation are dominated by mature,
quartzite conglomerates,
quartzites and muscovite-rich phyllites (Adolfsen, pers. commun.).
The G&rut Formation clearly has a provenance
more akin to a continental margin-type source
area than the dominantly mafic rocks of the underlying Qllve-Varaldsoy
Complex and the
Mundheim Group. Fragments of gabbro and
greenstone from the substrate are found only
locally. As the G&nut Formation shares the main
Caledonian compressional foliation and greenschist facies metamorphic assemblages with the
underlying rocks, it was deposited most likely
either shortly before or during the main collisional event at the time when the oceanic terranes were sufficiently close to the continent to
receive coarse-grained detritus from it. The only
sequence lying unconformably on ophiolitic rocks
in western Norway that resembles the Gr&rmt
Formation is the post-middle Llandoverian shallow-marine sediments of the Vaktdal Formation
in the OS Group of the Major Bergen Arc (Ingdahl, 1989). Hence, we tentatively suggest an
Early to Middle Silurian age for the G&rut Formation.
3. Discussion
As already outlined above, a major controversy
in the Caledonian geology of Scandinavia has
been whether the continental margin of Baltica
was affected by collisional tectonics prior to the
Scandian orogeny. In several recent plate reconstructions outlining the development of the Iapetus Ocean, Baltica has been shown as a continent
/ Tectomphysics
231
(1994)
71-84
79
that was surrounded by passive continental margins until it collided with Laurentia in the Late
Silurian (McKerrow et al., 1991; Scotese and
McKerrow, 1991). On the other hand, an early
Caledonian, Firmmarkian orogeny affecting the
continental margin of Baltica along most of the
Norwegian Caledonides have been argued by
Sturt, Ramsay and co-workers (including the first
author of this paper) in a number of papers since
the seventies (Sturt et al., 1978,1985, 1991; Sturt,
1984; and others). The geology in the outer
Hardanger-Sunnhordland
and Karmoy region has
been used as an argument for an early Caledonian, Finnmarkian orogeny. In the type area in
northernmost Norway, the existence of an early
Caledonian, Finnmarkian phase as defined by
Sturt et al. (1978) has been questioned; and much
of the deformation associated with the emplacement of the Seiland Igneous Province is of Proterozoic age (Pedersen et al., 1989b; Aitcheson,
1990; Daly et al., 1991).
In the central Scandinavian Caledonides, a
Late Cambrian-Early
Ordovician (510-490 Ma)
metamorphic event (Dallmeyer and Gee, 1986;
Mark et al., 1988) has affected rocks of the Seve
Nappes in the lower part of the Upper Allochthon which are suspected to have formed
parts of the outer margin of Baltica (Stephens
and Gee, 1989). This erogenic event is thought to
have originated by collision of an arc terrane with
the rocks inferred to belong to the outer margin
of Baltica (Dallmeyer and Gee, 1986). The metamorphic terrane including the eclogites in the
Seve Nappe was, however, emplaced onto the
Baltoscandian platform during Scandian thrusting
(Stephens and Gee, 1989). Torsvik et al. (1991),
on the basis of paleomagnetic data, suggested
that pre-Scandian deformation along the margin
of Baltica may have been associated with largescale anti-clockwise rotation of Baltica in the
Early to Middle Ordovician.
Brekke et al. (1984) used the stratigraphy and
geochemistry of the sedimentary and volcanic
rocks on Bomlo to suggest a plate-tectonic model
for the southwest Norwegian Caledonides. In this
model, the Lykling ophiolite and the Geitung
island arc were thought to have been accreted to
Baltica in the Tremadocian-Arenigian.
The Sig-
80
T.B. Andersen, A. Andresen / Tectonophysics
gjo, Vikafjord and Langevlg Groups which overlie the Lykling ophiolite and the Geitung island
arc were thought to record a convergent platemargin environment related to an E-dipping subduction zone under the western margin of Baltica
from the Middle Ordovician until Middle Silurian
times. The model was inspired by the ideas of
early Caledonian, Finnmarkian Group I ophiolite
accretion (Fumes et al., 1983, 1985; Sturt, 1984).
The stratigraphic succession as described by
Brekke et al. (1984) on Bornlo was partly based
on very uncertain lithostratigraphic correlation of
non-fossiliferous marbles and the limestones of
Ashgillian age in the Vikafjord and DyvikvBgen
groups (Fig. 3). Within the Siggjo volcanites (473
Ma) on Bornlo, an intraformational sequence of
conglomerates, sandstones, phyllites and limestone/marble
was regarded to be of Ashgillian
age (Brekke et al., 1984). These sediments are
overlain by a thick sequence of volcanics (the
Eriksvatn Formation) with geochemical characteristics similar to the Siggjo volcanics. Consequently they were believed to be of Silurian age
and assigned to the upper part of the Vikafjord
Group (Brekke et al., 1984). Similarly, the limestones and marbles on southeastern Bomlo and
Huglo (Fmrseth, 1982) were thought to be of
Ashgillian age. The deep-marine cherts, phyllites
and metagreywackes overlying the limestone/
marble sequence are in strike with the Langev%g
Group on southern Bomlo. This correlation suggested a Silurian age for the LangevPg Group
(Brekke et al., 1984), which is in faulted contact
with the fossiliferous Ashgillian rocks of the
Vikafjord Group in its type area on Born10
(Brekke, 1983). Comparison of the lithostratigraphy and geochemistry of the LangevPg Group on
Bornlo and the Torvastad Group on Karm0y (Fig.
2) shows many similarities; Pedersen and Dunning (in prep.) argue that these two units probably have a common origin in an Ordovician ( u 470
Ma) arc basin environment, but it is uncertain if
older continental crust formed part of the substrate of the arc. Feldspar Pb-isotope data from
the I-type granitoids
in the Sunnhordland
Batholith (unpublished report by Curti, 1988)
show a primitive mantle isotopic-ratio composition. This suggests that an older crustal compo-
231 (1994) 71-84
nent was insignificant in the source area for the
granitoid magmas that formed the Sunnhordland
Batholith (Andersen and Jansen, 1987), and that
contamination by old crust during ascent was
minimal.
To our knowledge, no record of elastic material other than that akin to the underlying ophiolites and ensimatic arc complexes occur in the
basal parts of the transgressive sequences in
southwestern Norway. Only the youngest parts of
these successions, including the Utslettefjell Formation (Fig. 3) deposited with an angular unconformity/ non-conformity
on the fossiliferous
Llandoverian rocks and the inverted Vardafjellet
Gabbro on Stord (Than et al., 1980, Andersen et
al., 1991b) and in the undated unconformable
G&rut Formation (see above) on Varaldsoy, contain elastic material that are exotic (quartzites
and granites) with respect to the ensimatic substrate. Similar elastic materials are also found
within the OS Group of the Major Bergen Arc,
where the Skarfjell Formation dominated by
quartz-rich sandstones and quartzite conglomerates, disconformably overlies fossiliferous Llandoverian phyllites (Ingdahl, 1989).
In southern Norway, evidence for a preSilurian erogenic event affecting Jotun-type continental basement (the Dalsfjord Suite) and cover
of continental
margin deposits (the Hsyvik
Group) is documented from Atloy in Sunnfjord
(Andersen and Daehlin, 1986; Brekke and Solberg, 1987; Andersen et al., 1990). This tectonothermal event is not dated and only a minimum
age provided by the unconformable Silurian Herland Group, is available. As pointed out above,
the status of the allochthonous continental crust
of the Dalsfjord Suite that has been correlated
with the Jotun Nappe, should be considered “suspect” with respect to Baltica as it is underlain
and separated from the Western Gneiss Region
by highly deformed rocks of the Kvamshesten
detachment
(Swensson and Andersen,
1991).
Consequently, a pre-Scandian orogeny affecting
undisputable Baltoscandian miogeocline or platform has not yet been documented with certainty
in this area, and the orogeny affecting the
Hoyvik/ Dalsfjord cover/ basement pair may have
occurred on a “Jotun microcontinent” separated
T.B. Andersen, A. Andresen / Tectonophysics 231 (I 994) 71-84
from Baltica by the highly deformed rocks of the
A&v011 group and the ophiolite/arc
lithologies
that occur structurally beneath the Jotun Nappe.
In the outboard terranes, the fossil-dated
Ashgillian to Llandoverian
sedimentary
sequences on Bornlo, Stord and Karmoy were deposited on a deformed substrate dominated by
ophiolitic and island-arc supracrustals and intrusions. On Karmoy, Ashgillian sediments (Skudesneset Group; Thon, 1980) postdate S-type granites of the West Karmoy Igneous Complex, which
are derived by partial melting of rocks with a
continental provenance (Sturt and Thon, 1978b;
Pedersen and Dunning, 1992). It is questionable
whether these rocks also could be derived by
partial melting of continental detritus carried
down an ensimatic subduction zone as suggested
by Pedersen and Dunning (1991). Apart from
these uncertainties, there is no evidence from
southwestern Norway that, with certainty, demonstrates that the composite ophiolite/arc
terranes were accreted to a continent (Baltica or
Laurentia) prior to their abduction onto Baltica
in the Late Silurian, Scandian orogeny. Thus, the
numerous stratigraphic and structural discontinuities recorded in the composite oceanic terranes
between Bergen and Karmoy (see above) must be
related to erogenic events that took place within
the Iapetus during construction of the composite
ophiolite/arc
terrane. This interpretation is in
agreement with traditional interpretations
of
Early to Middle Ordovician fauna1 provinciality
in the outboard terranes of the Scandinavian
Caledonides (Bruton and Harper, 1988).
Sturt et al. (1991) have reported recently on
stratigraphic relationships in the Otta area of
central southern Norway. The units discussed are
the VfigHmo ophiolite, the underlying Heidal
metasedimentary series and the Se1 Group, which
contains the fossiliferous Otta serpenitinite conglomerate at its base. The fossils are of Arenigian-Llanvirnian
age, and constitute a mixed
North American-Baltic
fauna (Bruton and Harper, 1981). There is little doubt that the serpentinite conglomerates are unconformable on the underlying, highly dismembered, Vlglmo ophiolite
(Sturt et al., 1991). Without discussing altematives, Sturt et al. (1991) conclude that the VHg%mo
81
ophiolite was accreted to Baltica prior to the
deposition of the Arenigian-Llanvimian
fossiliferous conglomerates. Both in forearc settings and
along transform/fracture
zones (Bonatti et al.,
1983; Saleeby, 1984) detrital serpentinites and
ultramafic protrusions are common, and serpentinite protrusions may reach shallow-marine conditions or even form islands. As also pointed out by
Pedersen et al. (1992), erosion and deposition of
ultramafites may occur without abduction and
should be considered in the interpretation
of
detrital serpentinites. During the buoyant rise of
the ultramafic rocks these are penetratively deformed together with parts of the oceanic crust.
The latter interpretation was suggested for detrital serpentinites that occur within the Silurian
abduction melange of the Solund-Stavfjord ophiolite complex of western Norway (Andersen et
al., 1990; Skjerlie and Fumes, 1990). If, however,
Sturt et al. (1991) are correct in their identification of a terrane-linking unconformity in spite of
the lack of continental debris in the fossiliferous
conglomerate, the relationships between the Jotun Nappe, the Heidal series, the VHgHmo ophiolite and the Se1 Group become critical and a third
tectonic interpretation may be suggested. If the
Jotun Nappe and other parts of the Precambrian
allochthonous gneisses in southern Norway are
exotic with respect to Baltica, the ophiolitic rocks
of the Otta area may have been accreted to a
“Jotun microcontinent” prior to the final Scandian emplacement of the composite terranes onto
Baltica. Thus, an early Caledonian event may
have affected the Jotun Nappe, its cover and the
Dalsfiord/Hoyvik
basement/ cover pair. These
units may, however, have been separated from
Baltica at the time of their deformation and only
been emplaced onto Baltica during the Scandian
orogeny.
We conclude that, from the available geological and geochronological data from the Sunnhordland-Hardanger
region there is no evidence
to suggest that the southwestern Norwegian ophiolitic terrane was accreted to Baltica before its
final emplacement during the Scandian orogeny
in the Middle to Late Silurian. It is suggested
that intra-oceanic plate convergence progressively
amalgamated ophiolitic and immature to mature
82
T.B. Andersen, A. Andresen / Tectonophysics 231 (1994) 71-84
arc complexes from the time ensimatic subduction was initiated in the Early Ordovician. The
amalgamation of this terrane was associated with
deformation and metamorphism which accounts
for the many stratigraphic discontinuities that
occur at several stratigraphic levels. With time, a
mature magmatic arc was formed within the Iapetus. It remains a possibility that continental crust
such as the Jotun Nappe and its sedimentary
cover may have constituted a part of this arc, and
that it formed part of very large system of composite terranes within the Iapetus Ocean (similar
to the Oliverian-Midland
Valley arc terrane of
McKerrow et al., 1991). The Iapetus finally closed
in the Silurian and the composite outboard terranes were emplaced onto Baltica during the
Scandian orogeny. Undisputable Baltic crust and
cover have apparently not been affected by Caledonian crustal shortening until the Silurian Scandian orogeny.
3. Ackn~nts
Financial support for this study has been provided through grants (44&l/002,
440.89/021,
440.90/007 and 440.92/002) from the Norwegian
Research Council of Science and the Humanities
(NAVF). Prof. John F. Dewey, Prof. Harald
Furnes and Dr. Stuart McKerrow suggested a
number of improvements to early versions of the
manuscript as did critical reviews by Dr. David
Roberts and Prof. D. Gee. The first author also
wishes to thank Prof. Dewey and the Department
of Earth Sciences at the University of Oxford for
providing good working facilities at a sabbatical
leave when the final version of this manuscript
was completed.
4. References
isotopicevidencefor exotic detritus
in the Kalak Nappe Complex, north NorwegianCaledonides.J. Geol. Sot. London, 147:923-926.
Andersen, T.B., 1989. Syn-deformational
emplacementof plutons in the CaledonianSunnhordlandBatholith,W. NorAitcheson, S.J., 1990. Nd
way. Geol. F&en. Stockholm F&h., 111: 375-378.
Andersen, T.B. and Dmhlin, PC., 1986. Basement-cover
kon-
takten mellom I-Biyvikgruppen og Dalsfjordsuiten p%Atloy,
en pre-kaledonsk avsetningskontakt. Geolognytt, 21: 13
(abstr., in Norwegian).
Andersen, T.B. and Jansen, 0.J., 1987. The Sunnhordland
Batholith, W. Norway: Regional setting and internal structure, with emphasis on the granitoid plutons. Nor. Geol.
Tidsskr., 67: 159-183.
Andersen, T.B., Fumes, H., Brekke, H., Sturt, B.A. and
Naterstad, J., 1984. The Torvikbygd Ophiolite-A
newly
discovered ophiolite fragment with an unconformable cover
sequence in the central Hardanger area, West Norway.
Nor. Geol. Tidsskr., 64: 69-73.
Andersen, T.B., Skjerlie, K.P. and Fumes, H., 1990. The
Sunnijord Melange, evidence of Silurian ophiolite accretion in the West Norwegian Caledonides. J. Geol. Sot.
London, 147: 59-68.
Andersen, T.B., Jamtveit, B., Dewey, J.F. and Swensson, E.,
1991a. Subduction and eduction of continental cmst: major mechanisms during continent-continent
collision and
erogenic extensional collapse, a model based on the south
Norwegian Caledonides. Terra Nova, 3: 303-310.
Andersen, T.B., Nielsen, P.E., Rykkelid, E. and Solna, H.,
1991b. Melt-enhanced deformation during emplacement
of gabbro and granodiorite in the Sunnhordland Batholith,
W. Norway. Geol. Mag., 128: 207-226.
Andresen, A., 1974. New fossil finds from Cambro-Silurian
metasediments on Hardangervidda. Nor. Geol. Unders.
Bull., 304: 55-60.
Andresen, A., 1978. Lithostratigraphy of the autochthonous/
parautochthonous
Lower Palaeozoic metasediments on
Hardangetvidda, South Norway. Nor. Geol. Unders. Bull.,
338: 59-69.
Andresen, A., 1982. Stratigraphy and and structural history of
the Lower Paleozoic metasediments on Hardangervidda,
South Norway. Ph.D. Thesis, Univ. California, 260 pp.
Andresen, A. and Faxseth, R., 1982. An evolutionary model
for the southwest Norwegian Caledonides. Am. J. Sci.,
282: 756-782.
Bonatti, E., Clocchiatti, R., Colantoni, R., Gehnin, R.,
Marinelli, G., Ottenello, G., Santacroche, R., Taviani, M.,
Abdel-Meguib, A., Assaf, H.S. and El Tahir, M.k, 1983.
Zarbargard (St. John’s) Island: An uplifted fragment of
sub-lied Sea lithosphere. J. Geol. Sot. London, 140: 677690.
Brekke, H., 1983. The Caledonian geological patterns of
Moster and southern Bemlo. Evidence for Lower Paleozoic magmatic arc development. Cand. real. Thesis, Univ.
Bergen (unpubl.).
Brekke, H. and Solberg, P.O., 1987. The geology of AtMy,
Sunnfjord western Norway. Nor. Geol. Unders. Bull., 410:
73-94.
Brekke, H., Fumes, H., Nor&s, J. and Hertogen, J., 1984.
Lower Palaeozoic convergent plate margin volcanism on
Bornlo, SW Norway, and its bearing on the tectonic environments of the Norwegian Caledonides. J. Geol. Sot.
London, 141: 1015-1032.
Bmton, D.L. and Bockelie, J.F., 1980. Geology and paleontol-
T.B. Anakrsen, A. Andresen / Tectorwphysics 231 (1%)
ogy of the Holonda area, western Norway-a fragment of
north America? In: D.R. Wones (Editor), The Caledonides in the USA. Proc. Int. Geol. Correlation Program-Caledonide
Orogen Project 27, Blacksburg, VA.
Dep. Geol. Sci., Va. Polytech. Inst. State Univ. Mem., 2:
41-47.
Bruton, D.L. and Harper, D.A.T., 1981. Brachiopods and
trilobites of the early Ordovician serpentinite Otta conglomerate, south central Norway. Nor. Geol. Tidsskr., 61:
153-181.
Bruton, D.L. and Harper, D.A.T., 1988. Arenig-Llandovery
stratigraphy and faunas across the Scandinavian Caledonides. In: A.L. Harris and D.J. Fettes (Editors), The
Caledonian-Appalachian
Orogen. Geol. Sot. London,
Spec. I’ubl., 38: 247-268.
Dallmeyer, R.D. and Gee, D.G., 1986. 4oAr/39Ar mineral
dates from retrogressed eclogites within the Baltoscandian
miogeocline; Implications for a polyphase Caledonian orogenie evolution. Geol. Sot. Am. Bull., 97: 26-34.
Dallmeyer, R.D., Andreasson, P.G. and Svenningsen, O., 1991.
Initial tectonothermal evolution within the Scandinavian
Caledonide Accretionary Prism: constraints from “?4r/
39Ar mineral ages within the Seve Nappe Complex, Sarek
Mountain, Sweden. J. Metamorph. Geol., 9: 203-318.
Daly, J.S, Aitcheson, S.J, Cliff, R.A., Gayer, R.A. and Rice,
A.H.N., 1991. Geochronological evidence from discordant
plutons for a late Proterozoic orogen in the Caledonides
of Finnmark, northern Norway. J. Geol. Sot. London, 148:
29-40.
Dunning, G. and Pedersen, R.B., 1988. U/Pb ages of ophiolites and arc-related plutons of the Norwegian Caledonides: implications for the development of Iapetus.
Contrib. Mineral. Petrol., 98: 13-23.
Foslie, S., 1955. Kisdistriktet Varaldsoy-Olve i Hardanger og
bergverksdriftens historie. Nor. Geol. Unders., 147: l-106
(in Norwegian).
Fumes, H., Skjerlie, F.J. and Tysseland, M., 1976. Plate
tectonic model based on greenstone geochemistry in late
Precambrian Lower Paleozoic sequences in the SolundStavtjord areas, West Norway. Nor. Geol. Tidsskr., 56:
161-186.
Furnes, H., Austrheim, H., Amahksen, KG. and Nordls, J.,
1983. Evidence for an incipient early Caledonian
(Cambrian) erogenic phase in southwestern Norway. Geol.
Msg., 120: 607-612.
Furnes, H, Ryan, P.D., Grenne, T., Roberts, D., Sturt, B.A.
and Prestvik, T., 1985. Geological and geochemical classification of the ophiolite fragments in the Scandinavian
Caledonides. In: D.G. Gee and B.A. Sturt (Editors), The
Caledonide Orogen-Scandinavia and Related Areas. Wiley, Chichester, pp. 657-670.
Faerseth, R., 1982. Geology of southern Stord and adjacent
islands. Nor. Geol. Unders. Bull., 371: 57-112.
Goldschmidt, V.M., 1912. Die kaledonische Deformation der
siid-norwegischen Urgebirgstafel. Skr. Vidensk. Selsk.,
Christiania 19, 11 pp.
Hurich, CA. and Kristoffersen, Y., 1988. Deep structure of
71-84
83
the Caledonide orogen in southern Norway: New evidence
from marine seismic refletion profiling. Nor. Geol. Unders., Spec. Fubl., 3: 96-101.
Ingdahl, SE., 1989. The Upper Ordovician-Lower Silurian
rocks in the OS area, Major Bergen Arc, Western Norway.
Nor. Geol. Tidsskr., 69: 163-175.
Krogh, E., Andresen, A., Bryhni, I., Broks, T.M. and Kristensen, S.E., 1990. Eclogites and polyphase P-T cycling
in the Caledonian Uppermost Allochthon in Troms, northern Norway. J. Metamorph. Geol., 8: 289-309.
Lutro, O., 1988. Lustrafjorden. Berggrunnsgeologisk kart 1417
I-M 1:50 080. Nor. Geol. Unders. Skr. 83, 39 pp.
McKerrow, W.S., Dewey, J.F. and Scotese, C.R., 1991. The
Ordovician and Silurian development of the Iapetus ocean.
Spec. Pap. Paleontol., 44: 165-178.
Milnes, A.G. and Koestler, A.G., 1985. Geological structure
of Jotunheimen,
southern Norway (Sognefjell-Valdres
cross-section). In: D.G. Gee and B.A. Sturt (Editors), The
Caledonide Orogen-Scandinavia
and Related Areas. Wiley, Chichester, pp. 457-474.
Mgrk, M.B.E., Kullerud, K.V. and Stabel, A., 1988. Sm-Nd
dating of Seve eclogites Norrbotten, Sweden-Evidence
for early Caledonian (505 Ma) subduction. Contrib. Mineral. Petrol., 99: 344-351.
Naterstad, J., 1976. Comments on the Lower Palaeozoic unconformity in western Norway. Am. J. Sci., 276: 385-390.
Naterstad, J. and Jorde, K., 1981. Basement-cover relationships in southern Norway-Hardangervidda
to Karmoy.
Uppsala Caledonide Symposium, Excursion Guide B6, 34
PP.
Nord%s, J., Amaliksen, KG., Brekke, H., Sutheren, R.J.,
Fumes, H., Sturt, B.A. and Robins, B., 1985. Lithostratigraphy and petrochemistry of Caledonian rocks on Bornlo,
southwest Norway. In: D.G. Gee and B.A. Sturt (Editors),
The Caledonide Orogen: Scandinavia and Related Areas.
Wiley, Chichester, pp. 679-692.
Pedersen, R.B. and Dunning, G., 1991. U/Pb datering av
oybuemagmatisme innenfor det serves&norske ofiolitt-terreng. Geonytt, 1: 91, 42-43 (abstr., in Norwegian).
Pedersen, R.B. and Dunning, G., in prep. Age relations
between ophiolite and island arc complexes: New U/Pb
ages from the ophiolitic terrane of SW NoMray. Contrib.
Mineral. Petrol., submitted.
Pedersen, R.B. and Fumes, H., 1991. Geology, Magmatic
affinity and Geotectonic environment of some Caledonian
ophiolites in Norway. J. Geodyn., 13: 183-203.
Pedersen, R.B. and Hertogen, J., 1990. Magmatic evolution of
the Karmoy Ophiolite Complex, SW Norway: relationships
between MORB-IAT-boninitic-talc-alcaline
and alkaline
magmatism. Contrib. Mineral. Petrol., 104: 277-293.
Pedersen, R.B., Furnes, H. and Dunning, G.R., 1988. Some
Norwegian ophiolite complexes reconsidered. Nor. Geol.
Unders., Spec. Fubl., 3: 80-85.
Pedersen, R.B., Fumes, H. and Thon, A., 1989a. Excursion
guide for the Karmoy Ophiolite Complex and associated
rocks. Intern. Publ. Dep. Geol., Univ. Bergen, 1: l-10.
Pedersen, R.B., Dunning, G.R. and Robins, B., 1989b. U-Pb
84
T.B. Andersen, A. Andresen / Tectonophysics 231 (1994) 71-84
ages of nepheline syenite pegmatites from the Seiland
Magmatic Province, N Norway. In: R.A. Gayer (Editor),
The Caledonide Geology of Scandinavia. Graham and
Trotman, London, pp. 3-8.
Pedersen, R.B., Fumes, H. and Dunning, G., 1991. A U/Pb
age for the Sulitjelma Gabbro, North Norway: further
evidence for the development of a Caledonian marginal
basin in Ashgill-Llandovery time. Geol. Mag., 128: 141153.
Pedersen, R.B., Fumes, H. and Bruton, D.L., 1992. Ordovician faunas, island arcs and ophiolites in the Scandinavian
Caledonides. Terra Nova, 4: 217-222.
Ragnildstveit, J., 1987. Geologien i Fusa omridet, Hordaland,
Vest-Norge. Cand. Scient Thesis, Univ. Oslo, 347 pp. (in
Norwegian with English abstr.1.
Reusch, H., 1888. B@mmeloen og Karmoen med omgivelser.
Nor. Geol. Unders., 422 pp. (in Norwegian).
Roberts, D., 1988. The terrane consept and the Scandinavian
Caledonides: a synthesis. Nor. Geol. Unders. Bull., 413:
93-99.
Roberts, D. and Gee, D.G., 1985. An introduction to the
structure of the Scandinavian Caledonides. In: D.G. Gee
and B.A. Sturt (Editors), The Caledonide Orogen: Scandinavia and Related Areas. Wiley, Chichester, pp. 55-68.
og strukturell
Rundhovde, E., 1987. Tektonostratigrafi
utvikling i Lukksund-omrbdet, soraust for Bjornafjorden,
Sunnhordland. Cand. Scient. Thesis, Univ. Bergen.
Saleeby, J.B., 1984. Tectonic significance of serpentinite mobility and ophiolitic melange. Geol. Sot. Am., Spec. Pap.,
198: 153-168.
Scotese, C.R. and McKerrow, W.S., 1991. Ordovician plate
tectonic reconstructions. In: C.R. Barnes and S.H. Williams
(Editors), Advances in Ordovician Geology. Geol. Sutv.
Can. Pap., 90-9: 271-282.
Sigmond, E.M.O., Gustavson, M. and Roberts, D., 1984.
Bergrunnskart over Norge-M.
1:l million. Nor. Geol.
Unders.
Skjerlie, K.P. and Fumes, H., 1990. Evidence for a fossil
transform fault in the Solund-Stavfjord Ophiolite Complex: West Norwegian Caledonides. Tectonics, 9: 16311648.
Sotli, A., Naterstad, J. and Andresen, A., 1978. Structural
succession in a part of the outer Hardangerfjord area,
West Norway. Nor. Geol. Unders. Bull., 343: 39-51.
Stephens, M.B. and Gee, D.G., 1989. Terranes and polyphase
accretionary history in the Scandinavian Caledonides.
Geol. Sot. Am., Spec. Pap., 230: 17-30.
Strand, T., 1951. The Se1 and V&e map areas. Nor. Geol.
Unders. Bull., 178: 1-178.
Strand, T., 1964. Geology and structure of the Prestberget
area. Nor. Geol. Unders. Bull., 228: 289-310.
Sturt, B.A., 1984. The accretion of ophiolitic terranes in the
Scandinavian Caledonides. Geol. Mijnbouw, 63: 201-212.
Sturt, B.A. and Thon, A., 1976. A comment on “The age of
erogenic deformation in the Sweedish Caledonides”. Discussion. Am. J. Sci., 276: 385-390.
Sturt, B.A. and Thon, A., 1978a. An ophiolite complex of
probable early Caledonian age discovered on Karmoy.
Nature, 275: 538.
Sturt, B.A. and Thon, A., 1978b. A major early Caledonian
igneous complex and a profound unconformity in the
Lower Paleozoic sequence of Karmoy, southwest Norway.
Nor. Geol. Tidsskr., 58: 221-228.
Sturt, B.A., Pringle, I.R. and Ramsay, D.M., 1978. The Finnmarkian phase of the Caledonian Orogeny. J. Geol. Sot.
London, 135: 597-610.
Sturt, B.A., Roberts, D. and Furnes, H., 1984. A conspectus
of Scandinavian Caledonian ophiolites. Geol. Sot. London, Spec. Publ., 13: 381-391.
Sturt, B.A., Andersen, T.B. and Furnes, H., 1985. The Skei
Group, Leka: an unconformable elastic sequence overlying
the Leka Ophiolite. In: D.G. Gee and B.A. Sturt (Editors),
The Caledonide Orogen: Scandinavia and Related Areas.
Wiley, Chichester, pp. 395-405.
Sturt, B.A., Ramsay, D.M. and Neuman, R.B., 1991. The Otta
conglomerate, the Viglmo Ophiolite-further
indications
of early Ordovician orogenesis in the Scandinavian Caledonides. Nor. Geol. Tidsskr., 71: 107-115.
Swensson, E. and Andersen, T.B., 1991. Contact relationships
between the Askvoll group and the basement gneisses of
the Western Gneiss Region (WGR), Sunntjord, Western
Norway. Nor. Geol. Tidsskr., 71: 15-27.
Thon, A., 1980. Steep shear zones in the basement and
associated deformation of the cover sequence on Karmoy,
SW Norwegian Caledonides. J. Struct. Geol., 2: 75-80.
Thon, A., 1985. Late Ordovician and Early Silurian cover
sequences to the west Norwegian ophiolite fragments:
stratigraphy and structural evolution. In: D.G. Gee and
B.A. Sturt (Editors), The Caledonide Orogen: Scandinavia
and Related Areas. Wiley, Chichester, pp. 407-415.
Thon, A., Magnus, C. and Breivik, H., 1980. The stratigraphy
of the Dyvikvagen Group, Stord: A revision. Nor. Geol.
Unders. Bull., 359: 31-42.
Torsvik, T.H., Ryan, P.D., Trench, A. and Harper, D.A.T.,
1991. Cambrian-Ordovician
Paleogeography of Baltica.
Geology, 19: 7-10.