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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,

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Presentation on theme: "Cratonic keels and a 2-layer mantle tested: Miles Osmaston Mantle expulsion during Arabia-Russia closure linked to westward enlargement of the Black Sea,"— Presentation transcript:

1 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

2 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

3 Opening of the western Black Sea 350km

4 Vrancea seismicity M>3.0 (Sperner et al 2001) Vrancea seismicity and shear line? 180 km ? Moesian ‘indenter’ microcraton mid-K closure Vrancea Transylvania

5 S.Karamata (2006) cites this as a part of the dextral shear line after Kemenci & Canovic 1997 Beograd Dextral shear zone N of Belgrade

6 The dextral link with the Alps The link with the Alps (Burchfiel)

7 = Motion 1 of Adria/Italy – km to WNW - Oligocene W Alps from Osmaston - submitted Final construction of the Western Alps 1

8 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 Subducting plate down-bend

9 Basal subduction tectonic erosion (STE): its large scale action Basal STE: its large-scale action

10 Apennines - preparation (seen as widespread sub-CCD turbidites)

11 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?

12 Apennines - construction Development of slab pull

13 Tyrrhenian downbend basins? Aeolian arc After Gamberi & Marani 2006 Downfaulting 100 km (a pseudo-trench?)

14 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 km

15 Seismicity Wortel & 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

16 Did Tyrrhenian slab pull drive the swing of Corsica-Sardinia? from Geological Map of Europe 1:5M, 2005

17 Opening of the western Black Sea - reprise 350km

18 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

19 Apparently these two primary directions were indeed operative in Apennines construction Guisy Lavecchia 1988

20 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


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