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)
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