Phanerozoic foldbelts and volcanic passive margins a causal relationship

1
Phanerozoic foldbelts and volcanic passive
margins a causal relationship?
E.R. Lundin A.G. Doré
NGU
Geological Survey of Norway
2
Layout

• Atlantic volcanic margins
• N Atlantic Igneous Province
• Iceland hotspot
• A model for volcanic margins
• Arctic and NE Atlantic similarities

3
Atlantic volcanic passive margins

• Typically attributed to abnormally hot
  asthenosphere
• NE Atlantic Iceland plume
• C Atlantic no obvious candidate
• S Atlantic Tristan plume

• Volcanic margins dominate

• Constitute part of Large Igneous Provinces (LIPs)

?
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Volcanic margin
After Eldholm et al, 1995
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NE Atlantic an archetype volcanic margin with a
classic hotspot (Iceland)

• Common assumptions
• Iceland hotspot is underlain by a plume (tail)
• The plume is deeply rooted and fixed
• NAIP was caused by the ancestral Iceland plume
  head
• The plume induced break-up
• Points which we questioned and which led to our
  hypothesis

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NAIP and Iceland plume (spherical plume head)
From White McKenzie (1989)
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NAIP and Iceland plume(subvertical mantle
sheets)

• 2000 km NW belt
• 2000 km NE belt
• Iceland pinpoint

From Smallwood White (2002)
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NAIP magmatism
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Transient rift - NAIP phase 1 (c. 62-58 Ma)
From Lundin Doré in press)
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Icelands hotspot track ?
Calculated tracks shown
The GFR is to a first order linear and symmetric
Hotspot has not been east of its current position
Purple Forsyth et al., 1986. Yellow Lawver
Müller, 1994
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• Modelling of the N Atlantic, using palaeomagnetic
  data and magnetic anomaly fits

Relative fits and global PM data after Torsvik et
al, 2001, Torsvik Van der Voo, 2002
12

• PM data - hotspot under N Greenland at 55 Ma if
  fixed

• Greenland and Eurasia have moved north (c. 600
  km)

Relative fits and global PM data after Torsvik et
al, 2001, Torsvik Van der Voo, 2002
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Can one generate the GFR with a fixed plume?

Vink, 1982
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Requires that plume (pin-point) drifts in the
same direction as, and in concert with, the plates

Vink, 1982
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If so, plate tectonics is at least controlling
the surface distribution of magmatism

Vink, 1982
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We argue that

• Iceland formed in situ on plate boundary, i.e. is
  not fixed
• Symmetry of GFR
• Lack of geologic evidence for a hotspot track
• Iceland is not underlain by deep plume
• Seismic tomography
• Plate tectonics governed distribution of NAIP
  magmatism
• Strong top down control

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It has been suggested that

• Thick GFR crust - melting of steeply dipping
  oceanic slab in suture (Foulger et al, 2002,
  2003)
• Eclogites may be a critical input to mantle
  peridotite for producing LIPs (Yaxley, 2000,
  Cordery et al, 1997)
• Typically thought to be recycled from core-mantle
  boundary
• Orogenic roots contain eclogitized material
  (e.g. Ryan 2001)
• Present along Phanerozoic fold belts

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We wonder

• Is it possible that eclogites from orogenic roots
  can have fertilized the mantle and indirectly be
  the cause of volcanic margins?

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Ryan Dewey, 1997
Austrheim, 1992
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What happens to delaminated eclogitized
roots? Are they necessarily lost to the system
or can they travel with the lithosphere and later
be incorporated into melts during break-up?
?
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Subducted slabs, detached from the lithosphere,
lie horizontally above the 600 km discontinuity
beneath the Carpathians (Blue).
From Wortel Spakman, 200l
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How can our concept be tested?

• A look along the Atlantic margins

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180 m.y. reconstruction

• Volcanic margins (red)
• re-opened (eclogitized) Phanerozoic foldbelts
• Non-volcanic (blue)
• where cratons were cut
• along Archean fold belts,
• where Phanerozoic foldbelts were crossed at
  high angle

From Lundin Doré, in press
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Does this make sense?

• UHP eclogites are mainly restricted to
  Neoproterozoic and Phanerozoic fold belts
• Earths temperature gradient was too high before
• A possible reason for not having eclogitic roots
  under Archean mobile belts

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Is there a correlation in the Arctic? Eurasia
Basin non-volcanic Canada Basin
volcanic? Any relationship to the Ellesmerian
fold belt?
From Lundin Doré, in press
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Some Arctic - NE Atlantic comparisons
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Early -mid-Cretaceous Arctic LIP (Maher, 2001)
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Magnetics and Ellesmerian Orogeny
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Magmatism vs Ellesmerian Orogen
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Greenland - Faroes Ridge
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GFR versus Alpha-Mendelev Ridge area
Greenland-Faroes Ridge
Alpha-Mendelev Ridges
1100 km
1100 km
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Crustal configurationGreenland-Faroes Ridge vs
Alpha Ridge
From Weber, 1990
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Subsidence comparisons (Sclater, 1977 Bott,
1983)
From Weber, 1990
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Alpha-Mendelev Ridge

• Strikingly analogous to Greenland-Faroes Ridge
• Crustal configuration
• Subaerial construction
• Presumably formed by same process (Weber, 1990)
• Can the Arctic provide a further test of the
  eclogitized root concept?
• Are the Canada Basin margins volcanic?
• Was the Ellesmerian root eclogitized?

35
Conclusions

• Iceland formed in situ, on the plate boundary
• So did several other Atlantic ridge-centred
  hotspots
• Iceland is neither deeply rooted, nor fixed
• NAIP magmatism
• 2 magmatic events oriented at nearly right angles
• Distribution can be related to plate tectonics
• Suggestive of top down control
• Eclogitized orogenic root concept
• Reasonable correlation in Atlantic
• A hypothesis to test in Arctic