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
OUTBOARD ACTIVITY:
From the Ægir Sea to the
Iapetus and Tornquist Oceans
The oldest supra-subduction zone
ophiolites and island-arc complexes
in the Scandinavian Caledonides
(`Group 1´) formed in this time-span
in the Early to Middle
Ordovician (495 to 465 Ma) while
Baltica started to drift northwards
with velocities up to ~10 cm/yr
Plate-tectonic velocities
of Baltica quantified
by pal-mag. data
QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture.
(Torsvik & coworkers)
Timanian
QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture.
From: Torsvik & Rehnström 2002
Nordkapp
The
Scandian
produced a
Evidence
forcollision
Early-Caledonian
nappe stackand
which
can be tracedis
deformation
metamorphism
along theinentire
belt: Theterranes
Lower,
common
the outboard
Middle,
Upper and
from Nordkapp
to Uppermost
Stavanger
allochtons
Example, Uppermost allochthon, Troms
30 E
70 N
Tromsø
The outboard terranes:
Upper and Uppermost
Allochthons
65 N
(Upm A): continental margin rocks
Trondheim
including marbles of
Laurentian (?) origin;
composite batholiths;
ophiolite/island-arc rocks,
para/orthogneisses with
Proterozoic (?) protoliths
(Up A): mostly ophiolites primitive
Bergen
Oslo
60 N
Stavanger
10 E
island-arcs, mature magmatic
arcs, associated metasediments
(late Cambrian-early Silurian)
Local Proterozoic basement
Early-Caledonian events; where and when?
460 Ma
Middle Ordovician
Corfu et al. in 2006, in press
Tromsdalstind eclogite
These events clearly occurred outboard of Baltica, and the rocks containing
their record was emplaced ‘piggy-back’ during the Scandian collision
Middle Ordovician unconformity over the Lyngen ophiolite (Up Alloch)
Eclogite facies metamorphism and deformation in the Tromsø region (Upm Alloch)
Corfu et al. 2003
`Group 1´ type ophiolites and island-arc complexes:
• Situated within the Upper Allochton between Karmøy
in the south and Lyngen in the north
• Ages spanning 495 to 465 Ma (within uncertainty)
with the Leka, Karmøy ophiolites as the oldest and
arc-plutons and volcancs as the youngest
• Both spreding axis and arc-magmatism
have geochemical subduction zone signatures
Lyngen
Narvik
Leka
Gjersvik
Trondheim area
Otta-Foldal
Roberts et al. 2002
Subduction polarity
away from Baltica, eventually
build-up of mature arcs
Bergen
Bømlo/Stord
Karmøy
AGE OF GROUP-1 OPHIOLITES/ISLAND -ARCS
From: Pedersen 1992
From: Roberts et al. 2002
A slide with Norwegian ophiolite summary
Nordkapp
70 N
Tromsø
30 E
Evidence for pre - Scandian
deformation and metamorphism is
common in the outboard terranes
from North-Cape to Stavanger
Example, North Cape
The outboard terranes:
Upper and Uppermost
Allochthons
65 N
(Upm A): continental margin rocks
Trondheim
including marbles of
Laurentian (?) origin;
composite batholiths;
ophiolite/island-arc rocks,
para/orthogneisses with
Proterozoic (?) protoliths
(Up A): mostly ophiolites primitive
Bergen
Oslo
60 N
Stavanger
10 E
island-arcs, mature magmatic
arcs, associated metasediments
(late Cambrian-early Silurian)
Local Proterozoic basement
The North Cape story, when? Sedimentation until Early Silurian (Aeronian-438 Ma);
syn-tectonic gabbro and granites (438-433 Ma);
Peak Barrovian metamorphism (~436 Ma)
RAPID TECTONIC EVOLUTION!
Corfu et al. in 2006, in press
Syn-tectonic gabbro
Sil
North cape
Kya
Staur
Gar
Syn-metamorphic granite
Andersen 1981
Early-Caledonian events; where? The Honningsvåg Igneous Complex
has primary magnetization and is well dated (437.5-438.9 Ma)!
Flysch sedimentation, deformation, plutonism and
metamorphism of early Silurian age near North Cape
Kirkland et al. 2005
440 Ma
The ‘Finnmarkian’ orogeny as originally proposed
by Sturt, Ramsay and co-workers (including me) does
not exist. The ‘Finnmarkian’ complexes comprise
late-Proterozoic rocks related to the Timanian
orogeny and pre-Caledonian rifting (now
positioned in the Middle Allochthon) as well as
overlying outboard rocks (Magerøy, Hellefjord,
Lyngen) that belongs to the Upper Allochthon
The HIC palaeomagnetic data from Torsvik et al. 1992,
reinterpreted with the new precise U/Pb ages from:
Corfu et al. 2006, JGS (in press)
THESE DATA SUGGEST THAT THE POSITION OF THE MAGERØY ROCKS
IN THE LOWER SILURIAN WAS EQUATORIAL, AND MOST LIKELY CLOSE
TO THE LAURENTIAN MARGIN
MATURE ISLAND-ARC
VOLCANIC AND COMPOSITE
PLUTONIC COMPLEXES
BUILD DURING THE MIDDLE
TO LATE ORDOVICIAN
Bindal-Helgeland
Smøla-Hitra
Up Hovind Gp.
Sunnhordland
First Scandian HP metamorphism ~ 424 ± 5Ma
Outboard activity related to magmatic arcs and back-arc
spreading in the Iapetus ocean
U/Pb ages of intrusives and some volcanics,
compiled by Corfu et al. 2006, in press.
Closure of the Tornquist Ocean
“Soft docking” of Avalonia
before the Late Ordovician ?
INTRA-ARC INCONFORMITIES
BELOW MID-LATE SILURIAN
OR DEVONIAN CONGLOMERATES
(UCF-3) IN SUNNHORDLAND
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EARLY-CALEDONIAN (PRE-SCANDIAN)
TECTONIC EVENTS ALONG THE
CALEDONIAN MARGIN OF BALTICA?
1) W-Finnmark, type area for ‘Finnmarkian’
now discredited. Caledonian deformation and
metamorphism Finnmark is Scandian
2) Nordbotn (~500 Ma eclogites, these need
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3
to be dated again by more precise methods)
3) Seve-Jämtland (~454±4 Ma eclogites
same age as Tromsø! Are these really in
rocks of Baltic origin or are they outboard?)
4) Otta-Foldal-Røros (pre-470 Ma)
5) Atløy, W. Norway (Ar-450 Ma + strat.)
6) Jæren (eclogites of unknown age in Jotun
nappe type rocks, same as Bergen eclogites, ie.
early-Scandian or Baltica-Avalonia collision?)
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7) Stratigraphy in foreland, clastic
cromite, most likely from ophiolite in the lower
middle Ordovician?
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6
The telescoped Caledonian
margin of Baltica
Stratigraphic (ucf + fossils) and geochronological evidence (Ar)
for an early Caledonian event at 450 Ma, Sunnfjord area, W.Norway
443 Ma
Silurian fossils
older than
450 Ma
1640 Ma
428 Ma
5 km
Brekke and Solberg 1987
Andersen et al. 1990, 1998,
Eide et al. 2000
Def/met
450 Ma
Early-Caledonian events; the Baltica-Avalonia assembly
Tornquist Sea closure by
subduction under E-Avalonia
in ~455-440.
Geological evidence?
Fauna provinciality between
Baltica and Avalonia
disappears
Mid-Ordovician metamorphic
ages (Ar) in North-Sea
basement
Subduction magmatism
in England - Wales
Kinnekulle K-bentonite
a ~455Ma supervolcano eruption producing
~1000km3 ash
Deformation/metamorphism
in nappes of SW.Norway
(Atløy, Jæren)?
From Torsvik & Rehnström 2003
IAPETUS IS CLOSING AND CONTINENTAL
COLLISION TAKES OVER FROM THE WENLOCK
THE LATE-SILURIAN
FULL SCALE COLLISON
BETWEEN BALTICA AND
LAURENTIA