Tertiary tectonics of Svalbard

• Introduction and talk objectives.
• Review of geologic history and richness.
• Description of Tertiary tectonics on a regional scale.
• Debate on timing of fold-thrust development.
• Plate tectonic setting.
• Description of major Tertiary tectonic elements.
• Conclusions as to what influenced this particular case history.
  

• 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 belt.

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 basin development.

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).

Carboniferous rifting:

• 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 550-350)
  • extensive nappe formation
  • possible terrane juxtapositioning.
  • emplacement of Motellafjellet eclogites and blueschists.
• Vendian diamictites (Harland, 1997 and many other publications).
• Grenvillian Nappes (Bjornerud, 1990).

Three major components:

• Tertiary fold-thrust belt.
• Forlandsundet and Renarodden hinterland grabens and the SEDL fault zone
• Billefjorden and Lomfjorden reactivation zones.

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 zone.
• Broggerhalvoya termination and anomaly.

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 (Nottvedt).
• fission track dating (Blythe and Kleinsphen, 1995).

My conclusions:

• 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.

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 extension
chron 31-25	69 - 59 Ma	35 km dextral and 12 km contraction
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 - 37 Ma	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.

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:

• examples.
• predictable detachment levels.
• fold and thrust duplexes.
• thin skinned emergence from underneath the foreland basin - Revneset area.

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 sinistral.

To the hinterland - Forlandsundet 'graben' and SEDL:

• structures indicating significant orogen-parallel motion.
• model for complex history.
• asymmetric character of the Forlandsundet 'graben'.
• Data from Sarstangen.

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 domains.
• 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.

Decoupling of orogen-parallel and perpendicular movements played a major role in this orogen. The pattern of decoupling evolved.

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.