A sub-crustal piercing point for North Atlantic reconstructions and tectonic implications Randell Stephenson et al.

A sub-crustal piercing point for North Atlantic reconstructions and tectonic implications Randell Stephenson et al.

a “tie” from one conjugate margin to another usually a geological feature at the surface or near-surface here (for the first time?), a lithosphere mantle feature is correlated from one conjugate margin to another A sub-crustal piercing point for North Atlantic reconstructions and tectonic implications

new data and something new discovered (in East Greenland) old data and an old discovery (in Scotland) a correlation of new with old some interesting things about this correlation A sub-crustal piercing point for North Atlantic reconstructions and tectonic implications

Skogseid et al., 2000 Ella Ø “converter” Flannan reflector

Schiffer et al., 2014, Geology

observed RFs structural model, based on WARR crust-upper mantle velocity model (Schlindwein, V., and Jokat, W., 1999; Voss, M., and Jokat, W., 2007) with 8 km thick 22° dipping slab with Vp=8.4 km/sec Schiffer et al., 2014, Geology

Flannan reflector

Flack and Warner, 1990

BIRPS Atlas II

DRUM BIRPS Atlas II

Flack and Warner, 1990

The Caledonian Orogeny: the triple convergence of Baltica, Laurentia and eastern Avalonia BIRPS Atlas II

Cocks & Torsvik, 2011

Thick black line (CDF): Caledonian Deformation Front (Dewey and Strachan, 2003; Gee, 2005), thick green line: Iapetus Suture (IS, Cocks and Torsvik, 2005; RIL, van Staal et al., 2009; TS, Pharaoh, 1999), purple: sketched major incipient rift zones (Roberts et al., 1999; Skogseid et al., 2000) Schiffer et al., 2014, Geology

Skogseid et al., 2000

Skogseid et al., 2000

Skogseid et al., 2000

Skogseid et al., 2000

Skogseid et al., 2000

Skogseid et al., 2000

The magmatism (13) is ascribed by many to the “Iceland plume”, which is thought to have arrived at the base of the lithosphere around this time. Palaeocene (60 Ma) Torsvik et al., 2004

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 and subduction into the lithosphere mantle is preserved even when complete continental break-up subsequently occurs nearby and that the polarity of the fossil subduction structure can be either towards (e.g. East Greenland) or away from (e.g. NW Scotland) the newly formed, nearby continental margin.

Conclusions 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 The Ella Ø-Flannan structure is older than the Mesozoic-Cenozoic extensional regime that culminated in continental break-up in the region in the Palaeocene. It probably comprises lower crustal material entrained within the mantle lithosphere during the Early Palaeozoic Caledonian Orogeny. The trace of the Ella Ø-Flannan mantle lithosphere structure has some interesting correlations with basin formation and magmatism in the North Atlantic.

Conclusions It coincides with, and probably is linked to, a number of complexities in the North Atlantic conjugate margin system, including extensive magmatism (and the formation of Iceland) and the anomalous rotation and preservation of the Jan Mayen continental fragment north of Iceland. Inherited structures deep within the lithosphere mantle play a role in magmatism and sedimentary basin formation (and dominate upper crustal structural reactivations).