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Stephenson_NAW2016

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A sub-crustal piercing point for North Atlanticreconstructions and tectonic implications
RandellStephenson et al.
A sub-crustal piercing point for North Atlanticreconstructions and tectonic implications
RandellStephenson et al.
a“tie” from one conjugate margin toanotherusuallya geological feature at the surface ornear-surfacehere(for the first time?), a lithosphere mantle feature is correlated from one conjugate margin toanother
A sub-crustal piercing point for North Atlanticreconstructions and tectonic implications
newdata and somethingnew discovered(in East Greenland)olddata and an old discovery (in Scotland)acorrelationof new with oldsomeinteresting things about this correlation
A sub-crustal piercing point for North Atlanticreconstructions and tectonic implications
Skogseidet al., 2000
Ella Ø “converter”
Flannanreflector
Schifferet al., 2014,Geology
Schifferet al., 2014,Geology
observed RFs
structural model, based on WARR crust-upper mantle velocity model (Schlindwein, V., andJokat, W.,1999; Voss, M., andJokat, W.,2007)with 8 km thick 22° dipping slab withVp=8.4 km/sec
Flannanreflector
Flack and Warner, 1990
BIRPS Atlas II
BIRPS Atlas II
DRUM
Flack and Warner, 1990
BIRPS Atlas II
The Caledonian Orogeny: the triple convergence ofBaltica,Laurentiaand easternAvalonia
Cocks &Torsvik, 2011
Thickblack line (CDF): Caledonian Deformation Front (Dewey and Strachan, 2003; Gee, 2005), thick greenline:IapetusSuture(IS, CocksandTorsvik,2005; RIL, vanStaalet al.,2009; TS, Pharaoh, 1999), purple: sketched major incipient rift zones (Roberts et al., 1999;Skogseidet al., 2000)
Schifferet al., 2014,Geology
Skogseidet al., 2000
Skogseidet al., 2000
Skogseidet al., 2000
Skogseidet al., 2000
Skogseidet al., 2000
Skogseidet al., 2000
Palaeocene (60 Ma)Torsviket al., 2004
Themagmatism(13) is ascribed by many to the “Iceland plume”, which is thought to have arrived at the base of the lithosphere around this time.
Schiffer et al. 2015. Geology
Schiffer et al. 2015. Geology
A numerical model of continental lithosphere shortening (convergence, seen here) followed by collapse and tectonic extension (next slide) demonstrating the emplacement of a fossil upper mantle lithosphere structure during the former and its preservation during the latter (cf. Petersen et al., 2010,Science).
A numerical model of continental lithosphere shortening (convergence, seen here) followed by collapse and tectonic extension (next slide) demonstrating the emplacement of a fossil upper mantle lithosphere structure during the former and its preservation during the latter (cf. Petersen et al., 2010,Science).
This is what we were just looking at (right), towards the end of the “convergence” phase. It is not meant as a realistic model of Caledonian collision in the proto-North Atlantic region. Below, the extension phase has begun (fast on the left, preserved mantle lithosphere structure dipping away from the new continental margin and slow on the right, with opposite polarity).
This schematic “accordion” model illustrates that entrained,eclogitised, lower crust emplaced during convergence andsubductioninto the lithosphere mantle is preserved even when complete continentalbreak-up subsequently occurs nearby and that the polarity of the fossilsubductionstructure can be either towards (e.g. East Greenland) or away from (e.g. NW Scotland) the newly formed, nearby continental margin.
An eastward dipping upper mantle structure discovered with receiver functions in East Greenland has a geometry and seismic attributes similar to the long known Flannan Reflector in the mantle lithosphere off northwest Scotland.These two structures can be correlated from one side of the North Atlantic Ocean to the other, representing what we think is the first sub-crustal “piercing point” recognised for reconstructing rifted conjugate continental margins.
Conclusions
TheElla Ø-Flannan structure isolder than the Mesozoic-Cenozoicextensional regime that culminated in continental break-up in theregion inthePalaeocene. It probably comprises lower crustal material entrained within the mantle lithosphere duringthe EarlyPalaeozoic Caledonian Orogeny.The trace ofthe Ella Ø-Flannanmantle lithosphere structure has some interesting correlations with basin formation and magmatism in the North Atlantic.
Conclusions
It coincideswith, and probably is linked to, a number of complexities in the North Atlantic conjugate margin system, including extensivemagmatism(and the formation of Iceland) and the anomalous rotation and preservation of the JanMayencontinentalfragment north of Iceland.Inherited structures deep withinthe lithosphere mantle playa role in magmatism and sedimentary basin formation (and dominate upper crustal structural reactivations).
Conclusions

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Stephenson_NAW2016