Transcript Slideshow 8Mb ppt

Cratonic keels and a 2-layer mantle
tested:
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
Miles Osmaston
First: What happens when cratons separate – Greenland-Eureka folding
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.
Opening of the western Black Sea
Vrancea
seismicity and shear line?
Vrancea seismicity M>3.0 (Sperner et al 2001)
180
km
Transylvania
Vrancea
mid-K
closure
?
Moesian ‘indenter’ microcraton
Dextral shear zone N of Belgrade
S.Karamata (2006) cites this as a part of the dextral shear line
Beograd
after Kemenci & Canovic 1997
The
dextral
link
with
the
Alps
The link with the Alps (Burchfiel)
Final construction of the Western Alps
= Motion 1 of Adria/Italy – 200-250km to WNW - Oligocene
W Alps
1
from Osmaston - submitted
Subducting plate down-bend
Stepfaulting mechanism of plate down-bend
causes…………
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
Basal STE: its large-scale action
Basal subduction tectonic erosion (STE): its
large scale action
Apennines - preparation
(seen as widespread sub-CCD turbidites)
Former extent of ‘Greater Adria’
Former extent(?) of
‘Greater Adria’
WHEN ADRIA WAS BEING STE-UNDERCUT IN CRETACEOUS but
was further East at the time
Apennines - construction
Development of slab pull
Downfaulting
Tyrrhenian
downbend
basins?
(a pseudo-trench?)
Aeolian arc
100 km
After Gamberi &
Marani 2006
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
Seismicity
Wortel & Spakman 2000
<40km
Jenny et
al 2006
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
Conclusions
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.
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