1

A new paradigm for the NE Atlantic Ocean

Gillian R. Foulger, Tony Doré, C. Henry Emeleus, Laurent Geoffroy, Laurent Gernigon, Ahmad Ghassemi, Richard Hey, Robert E. Holdsworth, Malcolm Hole, Ármann Höskuldsson, Bruce Julian, Nick Kusznir, Fernando Martinez, James H. Natland, Alex Peace, Kenni Petersen, Oliver Sanford, Christian Schiffer, Randell Stephenson and Martyn Stoker +…

1. Summary of the opening of the Labrador Sea/Davis Strait/Baffin Bay and NE Atlantic regions, the volcanic passive margins, Faroe-Shetland basin and crustal structure of the GIFR;
2. Presentation of new model of evolution of the GIFR based on idea that Icelandic-type lower crust is magma-inflated mid- and lower continental crust, possibly with some serpentinised mantle;
3. Numerical models including crack-propagation model (Ahmad) and thermo-mechanical model (Kenni);
4. Geochemistry;
5. Discussion, development of implications & conclusions.

2

3

Crustal fragmentation, magmatism, and the diachronous breakup of the Norwegian-Greenland Sea

Gernigon, L.; Franke, D.; Geoffroy, L.; Schiffer, C.; Foulger, G.; Stoker, M, +…

The Norwegian-Greenland Sea contains diverse tectonic regimes including microcontinents and conjugate volcanic passive margins ‘bridged’ to the south by the Greenland-Iceland-Faroe Ridge. The long period of rifting, structural style, and major breakup magmatism that included formation of seaward dipping reflectors distinguish the volcanic passive margins from non-volcanic margins. Thick sedimentary basin developed during drastic thinning of the continental crust associated with progressive exhumation of inherited, high-grade metamorphic rocks likely preserved beneath the seaward dipping reflectors. Breakup-related intrusions may localise deformation and guide the final axis of breakup along distal regions affected by pre-magmatic Late Cretaceous- Paelocene extension phase. Despite the common assumption that Norwegian-Greenland Sea breakup is essentially instantaneous, aeromagnetic data suggest it was diachronic, initiating isolated, segmented spreading centres. The early spreading system later developed and grew into atypical propagating systems that extended the time of breakup(s) and brought about step-by-step rupture of the lithosphere. The magnetic data also reveal an important mid-Eocene kinematic event at around magnetic chron C21r (46 Ma). This event coincides with the onset of diking, an increase in rifting and possibly oceanic accretion between the Jan Mayen microplate complex and the East Greenland margin. Complex rift reorganisation, deep inherited structures and magmatism likely influenced the final dislocation of the Jan Mayen microplate complex from Greenland in the Late Oligocene.

June 1: Final draft circulated to co-authors

end Aug: Definitely will be submitted by this time

4

Late Cretaceous-Cenozoic intraplate basin inversion in the North Atlantic-western Alpine-Tethys realm

Randell Stephenson, Scott Jess, Søren Nielsen, Alexander Peace & Christian Schiffer +…

Intraplate “basin inversion” occurs when normal faults developed during initial extensional basin formation are reactivated as reverse faults during post-rift periods of tectonic compression. Basin inversion is a good marker of (“far-field”) tectonic stress regime changes that are linked to plate boundary reorganisations. This premise is well-established in the literature: how Late Cretaceous- Palaeocene inversion of sedimentary basins has occurred in north-central Europe, for example, can be linked explicitly with the timing and style of plate break-up in the North Atlantic and its interactions with the Alpine-Tethys plate boundary of southern Europe. Periods of intraplate tectonics, marked primarily by structural inversion in initially extensional sedimentary basins in the North Atlantic realm, have been compiled from published literature. The focus is on the Late Cretaceous-Palaeocene, the Eocene and the Miocene. The aim is to establish a basis for investigating further if/how regional intraplate deformation/inversion in the North Atlantic-western Alpine-Tethys realm may be linked to rapid plate kinematic changes in this tectonic realm and, in turn, to plate tectonic boundary reorganisations taking place on a global scale.

August 25: draft for circulation

5

1. There are consistencies in the data for Baffin Island and Disko Island lavas that suggest derivation from mantle of higher than ambient TP and probably up to 1500°C.  The inability to produce anomalously high TP estimates for these lavas by olivine accumulation in a melt formed at ambient TP, coupled with TSp estimates and TOl-Sp up to 1450°C implies a mantle temperature at least 150°C greater than ambient mantle.  
2. The clear continuum of data that relates the Vaigat Formation picrites and overlying Maligat Formation lavas also suggest that the magmatic system developed at elevated TP.  The only detractors from this are a small number of glass analyses (9 in total) from Baffin Island that are suggesting of crystallization along a low temperature L+Ol+Pl cotectic.   However, these might also represent end-stage melts formed at shallow levels in the melting column.
3. For BPIP picrites there are inconsistencies between TOl-Sp and model Tsp, the former giving temperatures that are ~100°C hotter than would be expected from spinel alone.   Melt inclusions in olivine in lavas from MPLF picrites suggest TP~1480°C (Hole & Millett 2016) and we consider this the upper TP estimate for the BPIP.
4. For Iceland the situation is less clear.  PRIMELT3 solutions for Iceland are suspect, and there is little evidence from TSp or TOl-Sp for temperatures approaching those determined for picrites from the West of Greenland.  Consequently, there is little compelling evidence for TP>1450°C beneath modern Iceland assuming melting of dry peridotite.
5. Melting of a mixed pyroxenite-peridotite source at TP~1480°C cannot account for the geophysical estimates of crustal thickness beneath parts of eastern and central Iceland. Crustal thicknesses of up to 40 km most likely requires Iceland to be underlain by about 20 km of older crust.
6. Evidence from H2O contents of undegassed pillow glasses on Iceland suggests that their source might have been damp, a similar situation to that at the Azores.
7. If it is accepted that the maximum thickness of melt at Iceland rift zones is ~20km then all of the Iceland melt layer could have been formed by damp melting of mantle peridotite at TP ≤1450°C.  For 15 km of crust, this would drop to TP <1400°C.
8. Adding pyroxenite to a damp melt would not change significantly the TP needed for 15 or 20 km of crust because the solidi of the most likely compositions of pyroxenite in the source have similar slopes in P-T space to the damp solidus.  It is not, therefore possible to separate damp melting from that produced by melting of a hybrid pyroxenite-peridotite source.

6

Christian Schiffer, A.G. Doré, G.R. Foulger, Dieter Franke, Laurent Geoffroy, Laurent Gernigon, Bob Holdsworth, Nick Kusznir, Erik Lundin, Ken McCaffrey, Alex Peace, Kenni Petersen, Randell Stephenson, Martyn Stoker, Kim Welford +…

The North Atlantic (defined here as extending from the Iberia-Newfoundland conjugates to the north Norway-Greenland-Svalbard margins) is often regarded as a classic case of inheritance and as a model for the Wilson-cycle concept. This paper examines tectonic inheritance in the North Atlantic in two ways; 1) as a function of reactivation at different scales, ranging from lithospheric to local, and 2) in terms of development of the ocean and its margins through time.

7

Reykjanes Ridge Evolution by plate kinematics, propagating small-scale mantle convection, and a regional thermo-chemical mantle anomaly

Fernando Martinez & Richard N. Hey

Draft Abstract

1. The Reykjanes Ridge was originally one arm of a RRR triple junction that together accommodated opening between North America, Greenland and Eurasia.
2. It initiated as a linear spreading center over a regional mantle thermo-chemical anomaly with a strong gradient in properties leading to maximum melting beneath Iceland and grading to near normal crustal thickness south of the Bight FZ.
3. The linear ridge configuration and mantle gradient induced propagation of small-scale mantle convective cells along the Reykjanes Ridge axis forming the ridge flank V-shaped crustal ridges.
4. When the Greenland-North America plate boundary failed joining Greenland to North America, an abrupt 30° change in opening direction occurred across the Reykjanes Ridge as it became the new North America-Eurasia plate boundary.
5. The Reykjanes Ridge abruptly became segmented into an orthogonal ridge-transform stair-step pattern oriented in the new spreading direction.  The offset of ridge segments led to the segmented crustal accretion pattern of this phase of spreading.
6. The ridge segments promptly began to diachronously reorganize from north to south, eliminating the just-formed segmentation to re-establish the original linear configuration of the plate boundary.
7. This was likely driven by the persistence of the deep, low viscosity and voluminous asthenospheric melting regime which remained in a linear configuration following the abrupt fragmentation of the shallow lithospheric plate boundary to a stair-step pattern. 
8. As the plate boundary became linear, but now obliquely spreading, V-shaped crustal ridges formed again as a consequence of the axially-propagating small-scale convective cells.
9. The regional mantle thermo-chemical anomaly may have resulted from the slow advection deep mantle, as suggested in some seismic tomographic images, or it may have formed in the shallow mantle from ancient subduction events.
10. The regional mantle thermo-chemical anomaly may have existed passively below its solidus depth beneath the thick North American continental lithosphere long before breakup.
11. On continental rifting, this mantle anomaly would have been advected above its solidus, initiating melting and small-scale mantle advection to produce voluminous volcanism.
12. Propagation of small-scale convective cells along the rift and subsequent spreading ridge was driven by gradients in mantle properties (as inferred from the current axial depth profile and residual basement depth anomalies) and led to the linear configuration of the breakup and initial Reykjanes Ridge.
13. The model explains the initial distribution of voluminous volcanism following breakup, the pattern of residual crustal thickness anomalies on the ridge flanks and the current axial depth and crustal thickness variation along the Reykjanes Ridge without a mantle plume.

on target

8

The anomalous North Atlantic Region: Anomalous topography, crust and lithospheric mantle

Irina Artemieva, Hans Thybo & Alexey Shulgin

9

Alexander Peace, Dieter Franke, Tony Doré, Gillian Foulger, Nick Kusznir, Gregory McHone, Jordan Phethean, Sergio Rocchi, Christan Schiffer & Michael Schnabel +…

This paper reviews the dispersal of the Pangaea and Gondwana supercontinents and the relationship with large igneous provinces. The main finding of this work is that there exists a disparity between the initiation of rifting, breakup and the locations of large igneous provinces.

Aug 30: something to circulate around the wider North Atlantic meeting group

10

Nick Kusznir +…

end Oct: submission

11

D. Barrie Clarke & Erin K. Beutel

12

Mantle density and temperature structure of the North Atlantic ocean, Europe, and the Mediterranean

Alexey Shulgin & Irina Artemieva