Major tectonic processes illustrated with examples from the Geology of Norway

• Intro and overview of the Late Proterozoic to Permian tectonic evolution

• Baltica becomes a tectonic entity• The margins of Baltica• Early deformation along the

Caledonian margin• Ophiolites and island arcs• Towards continental collision and the

Scandian orogeny• Late to post-orogenic tectonic

processes• Late Palaeozoic continental rifting• Start of a new Wilson cycle

In the Middle Silurian, the Iapetus is rapidlyclosing, and deformation starts along theCaledonian margin of Baltica. The sketchprofile from southern Norway shows wherethe origin of the main tectonic units is shown.Foreland molasse sedimentation starts in thelate Wenlock showing that the topographywas growing in the hinterland

INFORMATION FROM SEDIMENTATIONAND DEFORMATION IN THE FORELAND

NOTICE: FIRST INDICATION OF INCREASED SEDIMENT INFLUX IN THE WENLOCK DEFORMATION STARTS IN THE LATEST SILURIAN

VOLCANIC ASH (BENTONITES) FROM LARGE CALC-ALKALINE ERUPTIONS ALONG THE TERMINAL ISLAND-ARCS IN THE CLOSING IAPETUS OCEAN

IN THE EARLY DEVONIAN THE NAPPE STACK IS ESTABLISHED

EXTENSION COMMENCES AT HIGH STRUCTURAL LEVELS ACROSS THE BELT

THE LOWER CRUST UNDERGOES HIGH-PRESSURELOW-TEMPERATURE METAMORPHISM

Scandian phase of the Caledonian Orogeny:Closure of ocean; Continental collision and Establishment nappe-stack

Top Uppermost AllochthonExotic rocks (Laurentian?)

Upper AllochthonOutboard, oceanic terranesEarly-Caledonian def/met complexes

Middle AllochthonMiddle AllochthonBasement cored nappes of Baltic originEarly-Caledonian def./met. complexes

Lower AllochthonLate-Proterozoic-Silurian cover

Base Autochthon-ParauthocthonBaltic cover and basement

Approxpin-line

Typical forelanddeformation, majordecollement on Mid. Camb - Lr Ordblack “alun” shales. Most of the forelandstrongly eroded, butpreserved downfaultedin the Permian Oslo-rift

From: Morley 1986

Example of balanced section,Asker, Oslo area

WE HAVE THE BEST EXAMPLES IN THE WORLD OF HIGH- ANDULTRA-HIGH PRESSURE METAMORPHIC ROCKS, STILL WE HAVE MANY PROBLEMS UNDERSTANDING THESE ROCKS!

The high and ultra-high-pressure rocks in Norway

HP-UHP rocksin W-Norway:

Large area,well exposed,great varietyprograde andretrograderelationships

T - 650 0C; P - 2.5 GPaEclogite w/polycrystallineqtz after coesite, loc.Barmen, Nordfjord

2 cm

Coesite in garnet

Coesitt-eclogiteNordfjord

Micro-diamond dissolved from garnet-kyanitegneiss at Fjørtoft (Dobrzhinetskaya et al. 1995)

Micro-diamond (c) in inclusion within spinel, in turn included in garnet (Van Roermundt et al. 2002)

ULTRA-HIGH-PRESSURE IN THE WGC, high-silica garnet (majorite) +10m

Southern WGR (HP) Nordfjord Region HP to UHP

[Labrousse et al. (in review), 1) staur - gar in KFAMASH (from Hacker et al. 2003, 2) hydrous solidus bio-granite, 3) Hydrous solidus musc-granite,

Data from a) Chauvet et al 1992, b) Hacker et al. 2003, c) Engevik et al. 2000 Outer eclogites , d) Krogh 1980 Inner eclogites e) Cuthbert et al 2000, Moldefjord data from Terry et al. 2000]

Age of coesite eclogite ? (gar, omp, phe, kya, coesite)

Unpubl. ages from David Root (2003) PhD, UCSB

AT CA 410 TO 405 Ma ULTRA-HIGHPRESSURE METAMORPHISMAFFECTS THE LOWER CRUST.RAPID EXHUMATION (5-10 mm/yr)OF THE HP-UHP CRUST STARTS BY A COMBINATION OF THRUST - STACKING, VERTICAL SHORTENING ANDEXTENSION AT HIGH CRUSTALLEVELS. DEVONIAN BASINS FORMAT THE SURFACE.

BAFFIN ISL

ELLESMERE ISL.

RINGNES

ISLS.

PRC WALES

ISL.

BOOTHIA UPLIFT

INGLEFIELDUPLIFT

Latest Silurian to early Devonian deformation far from the suture!AX HEIBERG ISL.

Major contractional events,Arctic Canada:Caledonian ≈ 425-400 MaEllesmerian ≈ 360-350 MaEureKan ≈ 65 - 35 Ma

ANALOGY WITH THE SCANDINAVIAN-GREENLAND CALEDONIDES:• pre-collision subduction polarity away from fast-moving plate• size• collision velocity ≈ 10 cm/yr• near orthogonal collision• duration (10-s of million years)• major continental plates

Outline of the N-Atlantic Caledonides in a tight late Silurian/early Devonian fitsuperimposed on the Himalaya-Tibetan Plateau Region topography

Late - to post-orogenic tectonic processes and exhumation mechanisms (ROCKS APPROACHING THE SURFACE)

1) EROSION (MINOR ON A REGIONAL SCALE)

2) THRUST STACKING + EXTENSION AND/OR EROSION(IMPORTANT FOR BRINGING HP AND UHP ROCKS NEXT TO EACH OTHER?

3) VERTICAL CO-AXIAL SHORTENING/HORISONTALSTRETCHING

(IMPORTANT FOR MID AND LOWER CRUST AFTER EXHUMATION TO AMPHIBOLITE FACIES)

4) HINTERLAND EXTENSION FORLAND SHORTENING(IMPORTANT AT AN EARLY STAGE OF COLLISION)

5) TRANS-TENSION(IMPORTANT)

• WHOLE-SALE EXTENSION BY PLATE-DIVERGENCE(IMPORTANT)