tectonics of Svalbard
Harmon D. Maher Jr., Department of Geography and Geology,
University of Nebraska at Omaha
- Introduction and talk objectives.
- Review of geologic history and richness.
- Description of Tertiary tectonics on a regional
- Debate on timing of fold-thrust development.
- Plate tectonic setting.
- Description of major Tertiary tectonic elements.
- Conclusions as to what influenced this particular
- provide an appreciation of the incredible
diversity and richness of geology and attendant research opportunities
that exist in Svalbard.
- discuss what factors and behavior were important
in shaping the Tertiary structures with an emphasis on the fold-thrust
Highlights of geologic history:
(from most recent
Isostatic response to glacial denudation (Blythe
and Kleinsphen, 1998).
Quaternary basaltic volcanism in the northwest
part of the islands.
Tertiary transtension, offshore basin
and continental margin formation.
Tertiary transpression (65-38 Ma), polyphase
development of variably decoupled transpressional welt, foreland
Late Cretaceous broad uplift and unconformity
formation, related to the High Arctic LIP.
Stable platform cover sedimentation until Upper
Cretaceous (circa 4-5 km thick).
- two major basins on Svalbard - the Billefjorden
and the St. Jonsfjorden.
- widespread rifting in what is now the Barents
Shelf area (Bashkirian-Asselian).
- rifting is atypical .
Local Serpukhovian folding and thrusting (Adriabukta
event of Birkenmajer, 1981).
Late Devonian Svalbardian contractional phase
(Lamar and others, 1986).
Devonian basin development > several kms
deep (gravitational collapse basins?).
Basement geology highlights:
- Polyphase Caledonian mountain building (from
- extensive nappe formation
- possible terrane juxtapositioning.
- emplacement of Motellafjellet eclogites and
- Vendian diamictites (Harland, 1997 and many
- Grenvillian Nappes (Bjornerud, 1990).
Description of Tertiary
tectonics on a regional scale.
Three major components:
- Tertiary fold-thrust belt.
- Forlandsundet and Renarodden hinterland grabens
and the SEDL fault zone
- Billefjorden and Lomfjorden reactivation
Fold-thrust belt components:
- basement involved antiformal stack.
- thin-skinned zone.
- Isforden fault zone.
- foreland and piggy-back basin.
- emergent structures to the E.
- Sorkapp termination and transfer to the Oyrlandet
- Broggerhalvoya termination and anomaly.
Debate on timing
of fold-thrust development.
Manby and Lyberis in three different articles
propose an Upper Cretaceous age, prior to the dextral separation
of the Barents Shelf and Greenland. They also suggest a minimum
of 80 km of shortening.
Evidence that major fold-thrust development
is Tertiary (Maher & others, 1995):
- 4 localities where Tertiary foreland basin
strata are involved in fold-thrust belt deformation.
- extensively and well exposed unconformity
at base of the Tertiary foreland sequence, without truncation
of any structures, and with regional geometry inconsistent with
a loading due to fold-thrust belt.
- Tertiary foreland sedimentation history consistent
with Tertiary deformation.
- divergence of west limb of the Tertiary Foreland
Basin and basement, and identification of underlying structures
- fission track dating (Blythe and Kleinsphen,
- there shouldn't be much of a debate.
- we can't rule out Cretaceous contraction
significantly to the west (in Greenland), but it didn't have
a sedimentologic signature.
Plate tectonic setting
during the Tertiary:
Basic two stage history:
Stage 1: circa 400 km dextral shear of Greenland
and Barents Shelf for anomalies 24-13, some 60-37 Ma.
Stage 2: change in pole of rotation, transtension,
formation of continental margin and development of oceanic crust
between Greenland and the Barents Shelf.
Are more complicated scenarios, ones that even
include minor sinistral movement. Below chart is from Skilbrei
(1993). Main point is that fairly complicated history possible,
but dextral transpression dominant.
| chron 34-31
|| 84 - 69 Ma
|| 170 km dextral and 20 km
| chron 31-25
|| 69 - 59 Ma
|| 35 km dextral and 12 km
| chron 25-24
|| 59 - 55 Ma
|| 42 km of shortening and
16 km sinistral
| chron 24-21
|| 55 - 49 Ma
|| 220 km dextral, 40 km contraction
| chron 21-13
|| 49 -
|| 270 km dextral
Harland gave birth to concept of transpression
for Caledonide structures, and Lowell applied it to the Tertiary
fold-thrust belt in developing the original formulation of a a
positive flower structure.
Description of major
Tertiary tectonic elements.
Basement involved antiformal stack structures:
- St. Jonsfjorden example.
- transgressed fault-propagation folds with
overlying folded/rotated thrusts.
- localized by the eastern margin of the St.
Jonsfjorden Carboniferous structure.
- associated backthrusts (Hauser).
Thin-skinned foreland zone:
- predictable detachment levels.
- fold and thrust duplexes.
- thin skinned emergence from underneath the
foreland basin - Revneset
Billefjorden and Lomfjorden fault zones:
- from N to S -> deeper to shallower exposures.
- BFZ and reactivation of a terrane boundary.
- interaction of basement and thin-skinned
tectonics (Bergh and Andresen).
- Lomfjorden Carboniferous and Tertiary reactivation
of a large basement syncline.
- If a strike-slip component it is arguably
To the hinterland - Forlandsundet 'graben'
- structures indicating significant orogen-parallel
- model for complex history.
- asymmetric character of the Forlandsundet
Overview of Tertiary kinematics:
- some 30-40 km of shortening across the width
of the island occurred.
- interpretation of fault-plane-striae plots
as bulk cataclastic strain in context of specific structural
- data from some 17 areas spanning the length
and width of Spitsbergen, > several thousand readings.
- Summary of results for the fold-thrust belt:
- consistent early phase (rotated) orogen oblique
(consistent with dextral setting).
- main phase orogen perpendicular.
- out of sequence phase again orogen oblique.
- the hinterland has its own unique signature.
- an evolving welt model with a twist - what
happens to taper angles with a hinterland localization of orogen
parallel shear zones.
Conclusions as to what
influenced this particular case history.
Decoupling of orogen-parallel and perpendicular
movements played a major role in this orogen. The pattern of decoupling
Weak surfaces played a major role in localizing
detachments and orogen-parallel motions. Weak surfaces include
stratigraphic horizons, basement faults, and structural zones
that evolved in the Tertiary (possible foreland migration of orogen-parallel
motions with time).
Reactivation and inversion of a Carboniferous
rift basin localized antiformal stack, influenced along strike
patterns and segmentation.
Foreland basin development played a role as
it became a big piggy back basin, and acted as a competent unit
forcing propagation underneath it.
Backthrusting and wedge insertion played a
critical role in distinct portions of the orogen (Hauser).
This was a low strain rate orogen, manifest
by cleavage duplexes, greater degree of basement involved folds,
and fold duplexes, and perhaps a larger taper angle.