Transcript Major tectonic processes illustrated with examples from the Geology

Major tectonic processes illustrated with
examples from the Geology of Norway
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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 rapidly
closing, and deformation starts along the
Caledonian margin of Baltica. The sketch
profile from southern Norway shows where
the origin of the main tectonic units is shown.
Foreland molasse sedimentation starts in the
late Wenlock showing that the topography
was growing in the hinterland
INFORMATION FROM SEDIMENTATION
AND 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-PRESSURE
LOW-TEMPERATURE METAMORPHISM
Scandian phase of the Caledonian Orogeny:
Closure of ocean; Continental collision and
Establishment nappe-stack
Top
Uppermost Allochthon
Exotic rocks (Laurentian?)
Upper Allochthon
Outboard, oceanic terranes
Early-Caledonian def/met complexes
Middle Allochthon
Basement cored nappes of Baltic origin
Early-Caledonian def./met. complexes
Lower Allochthon
Late-Proterozoic-Silurian cover
Base
Autochthon-Parauthocthon
Baltic cover and basement
From: Morley 1986
Typical foreland
deformation, major
decollement on
Mid. Camb - Lr Ord
black “alun” shales.
Most of the foreland
strongly eroded, but
preserved downfaulted
in the Permian Oslo-rift
Example of balanced section,
Asker, Oslo area
Approx
pin-line
WE HAVE THE BEST EXAMPLES IN THE WORLD OF HIGH- AND
ULTRA-HIGH PRESSURE METAMORPHIC ROCKS, STILL WE
HAVE MANY PROBLEMS UNDERSTANDING THESE ROCKS!
The high and ultra-high-pressure rocks in Norway
HP-UHP rocks
in W-Norway:
Large area,
well exposed,
great variety
prograde and
retrograde
relationships
T - 650 0C; P - 2.5 GPa
Eclogite
w/polycrystalline
qtz after coesite, loc.
Barmen, Nordfjord
2 cm
ULTRA-HIGH-PRESSURE IN THE WGC, high-silica garnet (majorite) +
10mm
Coesitt-eclogite
Nordfjord
Micro-diamond dissolved from garnet-kyanite
gneiss at Fjørtoft (Dobrzhinetskaya et al. 1995)
Micro-diamond (c) in inclusion within spinel, in turn
included in garnet (Van Roermundt et al. 2002)
Coesite in garnet
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-HIGH
PRESSURE METAMORPHISM
AFFECTS THE LOWER CRUST.
RAPID EXHUMATION (5-10 mm/yr)
OF THE HP-UHP CRUST STARTS BY A
COMBINATION OF THRUST - STACKING,
VERTICAL SHORTENING AND
EXTENSION AT HIGH CRUSTAL
LEVELS. DEVONIAN BASINS FORM
AT THE SURFACE.
Latest Silurian to early Devonian
deformation far from the suture!
INGLEFIELD
UPLIFT
BOOTHIA UPLIFT
BAFFIN ISL
Major contractional events,
Arctic Canada:
Caledonian ≈ 425-400 Ma
Ellesmerian ≈ 360-350 Ma
EureKan ≈ 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 fit
superimposed 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/HORISONTAL
STRETCHING
(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)
6) WHOLE-SALE EXTENSION BY PLATE-DIVERGENCE
(IMPORTANT)