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Cratonic keels and a 2-layer mantle tested:
Miles Osmaston
Mantle expulsion during Arabia-Russia closure linked to
westward enlargement of the Black Sea, formation of the Western Alps and
subduction of the Tyrrhenian (not the Ionian) Sea
Osmaston 2006
First: What happens when cratons separate?
The Greenland- Eureka folding
The early Arctic ocean was nearly surrounded by
cratons, so the flow of mantle to put under the opening Eurasia Basin ‘dragged’
Greenland’s keel northward in the Eocene, causing major folding across it’s northern
neighbours.
First: What happens when cratons separate – Greenland-Eureka folding
Opening of the western Black Sea
350km
Vrancea seismicity M>3.0 (Sperner et al 2001)
Vrancea seismicity and shear line?
180km
?
Moesian ‘indenter’ microcraton
mid-K closure
Vrancea
Transylvania
S.Karamata (2006) cites this as a part of the dextral shear line
after Kemenci & Canovic 1997
Beograd
Dextral shear zone N of Belgrade
The dextral link with the Alps
The link with the Alps (Burchfiel)
= Motion 1 of Adria/Italy – 200-250km to WNW - Oligocene
W Alps
from Osmaston - submitted
Final construction of the Western Alps
1
Stepfaulting mechanism of plate down-bendcauses…………
1. seismic coupling (alternate step-fault and interface slip)2. basal Subduction Tectonic Erosion (STE) - development
of flat subduction profiles
crust of upper plate
each step increment traps a sliver of upper
plate
downbend moves forward
Subducting plate down-bend
Basal subduction tectonic erosion (STE): its large scale action
Basal STE: its large-scale action
Apennines - preparation
(seen as widespread sub-CCD turbidites)
Final line of
subduction
downbend
Former extent(?) of ‘Greater Adria’
WHEN ADRIA WAS BEING STE-UNDERCUT IN CRETACEOUS but was further East at the time
Former extent of ‘Greater Adria’
trench line in
Cretaceous?
Apennines - constructionDevelopment of slab pull
Tyrrhenian downbend
basins?
Aeolian arc
After Gamberi & Marani 2006
Downfaulting
100 km
(a pseudo-trench?)
Overthrusting of Calabria-Peloritani
All have been overthrust from the direction of the Tyrrhenian Sea. This has induced strong epeirogenic response in blocks of mature continental crust, (which have not been displaced).
Episodes 2004
250km
SeismicityWortel & Spakman 2000
Jenny et al 2006
<40km
Where does >800km of slab length come from if it was Ionian?
Mainly intracrustal (thermal) epeirogenic adjustments following overthrusting
Did Tyrrhenian slab pull drive the swing of Corsica-Sardinia?
from Geological Map of Europe 1:5M, 2005
Opening of the western Black Sea - reprise
350km
1. Mantle flow expelled from between the converging Russia-Arabia cratons HAS driven the keel of Moesia westwards, and is still active (Vrancea).
2. In the Oligocene this action drove the Balkans ~200km westward. This built the Western Alps and started Apennines construction by reactivating Cretaceous subduction and triggering Tyrrhenian slab pull.
3. Since mid-Cretaceous or earlier, this action has driven or triggered E-W components of closure in Mediterranean belts.
4. N-S closure in the East was the primary agent, so N-S compression was present too.
Conclusions
Apparently these two primary
directions were indeed operative in Apennines
construction
Guisy Lavecchia 1988
So I conclude that the Earth does indeed have a 2-layer mantle
and(at least some) cratonic keels that
reach nearly to the 660.
Thank you