Fingered by the Plume

Obviously this is not Kistufell, this is the picturesque volcano of Esjan that is best viewed from Reykjavik with a beer in hand. I mixed up the volcanoes while speed editing.

In the last few years new data about the Icelandic mantleplume has emerged that forever has changed how we look at it, and how it affects Iceland.

In yon olden days, it was perceived through the eyes of the original plume model that was devised to explain the Emperor Seamount Chain and Hawaii. That means that it should have deep origin within the mantle, or even spring out from the boundary between the mantle and the outer core.

It was also believed that the Icelandic mantleplume would have emplaced a plume track in the same manner as the Emperor Seamount Chain. The idea was that it would be a remnant plume from the Alpha Ridge Large Igneous Province event that had meandered over to its current location via Greenland.

The only problem was that almost all evidence pointed away from this plume model as an explanation for Iceland. As science progressed it turned out that almost no mantleplume on earth behaves as the Emperor Plume does. It was the odd bird out and should never have been used as the defining plume for the mantleplume theory.

So, let us throw out the old and bring in the new and see where we stand.

Spinels and garnets on the plume

Something you will not find in Icelandic mantleplume derived lava, a 7.95ct Pink Spinel.

The first thing we need to do is to look at the general depth that the mantleplume burrows down to. The best way to do that is through petrochemical analysis of the lavas from Kistufell. The reason that it is best done from those lavas is that Kistufell is sitting on the centre point of the mantleplume upwelling and as such should contain the purest lavas if you wish for a high mantleplume derived magma origin of the lava.

Lavas from Kistufell shows that the plume derived magmas are like this: “The isotopic heterogeneity within the Iceland mantle plume may thus be viewed as a result of mixing between plume material rising from a layer of subducted slabs (which have partly maintained their geochemical integrity and heterogeneity) and lower-mantle material (FOZO) entrained in the initial stages of plume formation.” (Kresten Breddam, 2002, linked below)

The sentence above might be the most explosive sentence in contemporary volcanology. It is like someone had chucked the Tsar Bomba into the classical mantleplume model for Iceland. I will try to explain it by quoting myself… Massively.

“Kistufell is situated straight on top of the Icelandic mantleplume core. The petrochemical analysis gives at hand that a large part of the magma comes from the 670-kilometer discontinuity where it passes through subducted slab remnants and is consistent with a formative mantleplume in the lower mantle.

Kistufell is quite shy of photography. Image taken away from Kistufell.

Now, what on earth is the 670-kilometer discontinuity? Well, material above that has the spinel crystal structure and below you have perovskite structure. In short, if your basic magma has spinels in it you have magma from above the discontinuity. If you have a marked lack of spinels the magma formed deeper than the discontinuity.

And the Kistufell magma is poor in chromium spinels, and the few that are seems to have come from xenoliths from the magma conduits rather than from the basic basalt (ol-tholeiite). Also, the high amount of Sr points towards a deep source.

Now over to garnets, they form at about 35 to 45 kilometers’ depth, and the Kistufell lava is very poor in garnets, so it is safe to assume that the magma has formed below that. This differentiate the Kistufell (and other mantleplume volcanoes) from other Icelandic volcanoes far away from the plume core.

There are also inclusions of material that points to the formative mantleplume punching through a tectonic slab graveyard situated above the 670km discontinuity.”

Is there any evidence that the mantleplume is indeed formative? Yes, there is. The amount of spinels increases with the age of the lavas tested in Iceland. Or, in other words, the older magmas came from an increasingly shallow depth as we progress backwards in time.

As such the mantleplume is not more than 14 million years old, at least in a way that we define as a mantleplume. That puts quite a spanner in the Alpha Ridge Theory, or any other theory stating that the Icelandic Plume has meandered over from somewhere else.

Locating the plumehead

A nice hut if you wish to study Kistufell, it is apparantly not used by photographers…

Garnets fill yet another purpose, they are uniquely useful to decide where in Iceland the center of the plumehead lies. And it turns out that the further away you go from Kistufell, the more garnets you will find as you sample young lavas. The difference is not majestic, and there are anomalies.

There is a lower amount of Spinels in the southeastern quadrant of Iceland, and there is also a lower garnet count in a line that runs down via Eyjafjallajökull and Katla onwards down the Vestmannaeyjar Volcanic Line compared to volcanism west and northeast of Kistufell. There is also a low garnet line running to the North via the central volcanoes there.

This would indicate to any normal mind that there is a sub-crustal river of molten mantleplume derived magma flowing down to the south and to the north.

In Today’s Plume News

Plume fingers of Iceland. Image by Schoonman et al.

In a recently published paper by Schoonman et al titled: ‘Radial viscous fingering of hot asthenosphere within the Icelandic plume beneath the North Atlantic Ocean’, they presented a model discussing the formation of such sub-crustal rivers of magma.

The model is based on an old physics experiment where a less viscous fluid is injected into a more viscous fluid placed between two sheets of glass. In the experiment fingers of the less viscous fluid (more fluid) flows uniformly as tendrils (fingers) in all directions since the pressure is uniform due to the equidistance of the two sheets of glass.

In the real world, the pressure will be influenced by the thickness of the crust and crustal canyons giving differences in pressure.

In Iceland, the centre of the plumehead is at 35 kilometres’ depth below Kistufell. From there the naturally heat-buoyant plume derived magma will try to float towards shallower crustal parts following the path of least resistance.

The clearest visible finger follows the line via Eyjafjallajökull and Katla towards the WVL due to the crustal inverted canyons that have formed due to the spreading of Iceland. The bulk of this finger reconnects to the MAR SSW of Iceland, but a part of the finger splits off and meanders off towards Scotland.

This finger is interpreted in the paper as the reason that Northern Scotland is above the surface of the water since the buoyance of the hot magma would lift the crust upwards. The reasoning here is that the Scottish crust is not buoyant enough on its own, to be above ocean level.

There is also a large finger going northwards all the way to Jan Mayen where it forms a secondary plumehead. If there is further evidence of this being true, the Jan Mayen mantleplume will have been falsified. Time to test for spinel/garnet ratios on a line from Iceland to Jan Mayen methinks.

There is also a marked discontinuity towards Greenland negating any possibility that the plume has moved through Greenland to its current position since it would have left a remnant heat residual track. And there is just none to be had.

Now it is time to become critical of the paper. The authors indicate a very long finger running due east before it bends like a banana down the Norwegian coastline. They once again reason that what we see is distal plume derived magma lifting thin Norwegian crust upwards through heat buoyancy.

This seems to me to be a classic case of over-extending a valid model into a territory where it is no longer valid. Firstly, there is a marked discontinuity of the finger that is not explained. Secondly, they seem to forget that Norway is the leading edge of one of the world’s thickest crusts, the Baltic Shield. As such it is by far buoyant enough on its own to float above the oceanic surface.

So, what then would form the heat signatures we see? I will try to explain that. As the MAR split apart, it forms brand new crust that is pushing the Northern American continent apart from the Eurasian Continent.

This has two effects, one is that North America is moving to the south-southwest and that there is increased pressure on the western edges of the fairly immovable Eurasian continent. This has by now created what is believed to be proto-subduction faults. One of them is located near the Norwegian coastline.

It is as such far more likely that what we are seeing is that the subduction process has gone further than we previously believed and that the happy Norwegians will be the recipients of a few dozen explosive stratovolcanoes in a geological future.

Conclusion

Iceland, keeping Scots dry since 14 million years.

Even though the paper in my view is over-extending the model by putting a finger in the nether regions of Norway it represents a major breakthrough in our understanding of the size and distribution of the Icelandic mantleplume.

It puts the last nail in the coffin of the wandering plume theory and it neatly seems to explain away the Jan Mayen mantleplume. In the other direction, it shows that the future of Icelandic volcanism will run through the Vestmannaeyjar and reconnect to the MAR south of Iceland.

It also explains why we do not have kilt-wearing fish-humans wielding claymore’s at passing ships whilst they emit burbling noises from sheep-bladders.

All in all, it has been a good week in volcanology.

CARL REHNBERG

https://academic.oup.com/petrology/article/43/2/345/1550472/Kistufell-Primitive-Melt-from-the-Iceland-Mantle

http://www.sciencedirect.com/science/article/pii/S0012821X17301784

71 thoughts on “Fingered by the Plume

  1. Very interesting! So it means the Holuhraun magma came direct from the plume via Kistufell then? Also, is the Scotland plume finger related to the ancient volcanoes in that region (Glen Coe et al.)?

    • Hello!
      No, the Holuhráun lava took the scenic route. First it Went up into the magma reservoir of Kistufell, then it formed a dyke towards Bárdarbunga that entered the magma reservoir of that volcano. Then it meandered of to Holuhráun.

      Nope, the ancient volcanoes in Scotland are older than the Icelandic plume.

  2. Thanks for that. It all begins to make more sense, though still a vague view of things – and that’s no criticism at all, just an acceptance of this being a continued process of learning 🙂

    You say how the garnet distribution varies across regions, but *in* those regions how does it vary within different aged lava?

    Re Scotland, from my school geography I recall how Britain has tilted with the North rising and the South sinking. The explanation was always that happened as a result of the ice melt. The North is still rising. I wonder if that continued rising is momentum or maybe it’s at least partly due to the mantle plume effect?

    I wonder if there is any suggestion that the strength of the plume is increasing, stabilised, or declining?

    • The differentiation between more or less garnets does not have a lot to do with age. Instead that is more about the intermix ratio between MORB derived magma and Plume deriven magma. The MORB magma from the upper mantle is higher in garnets than the plume magma.

      The northern uplift is mainly due to isostatic rebound.

      The magma arrival from the plume has increased over time, so increasing.

      • Thanks 🙂 I wondered though if there was any indication of the amount of garnets in these other areas varying in different lava flows ie changing over time, thus indicating a change of location of the plume. Or maybe the info is generalised over all lava flows in each location.

        • The fun part is that Iceland is almost stationary, and the same goes for the plume.
          The center of attention has been at Vatnajökull for a very long time as evidenced that the crust is thickest around that part. It is the spread of the MAR that enlarges Iceland, and it has spread from the site of the plume for at least 6 million years (probably longer).

  3. “This finger is interpreted in the paper as the reason that Northern Scotland is above the surface of the water since the buoyance of the hot magma would lift the crust upwards. The reasoning here is that the Scottish crust is not buoyant enough on its own, to be above ocean level.Now it is time to become critical of the paper. The authors indicate a very long finger running due east before it bends like a banana down the Norwegian coastline. They once again reason that what we see is distal plume derived magma lifting thin Norwegian crust upwards through heat buoyancy.”

    Can these plume fingers cause volcanism in Scotland and Norway? At http://www.mantleplumes.org/Scandes.html more about a plume below Norway.

    • I never use http://www.mantleplumes.org as a source. They are alt-fact, bordering on religious belief in plumerisms.

      It is highly unlikely that the plume finger would cause volcanism in Scotland. And since there is no plumefinger under Norway it will not cause eruptions there. Subduction melt volcanism in a distant Norwegian future is something completely different.

        • That is not a plume. It is caused by a bit of extension in the crust, caused by the pressure from Spain (I think). The line of extensions extends from southeast Spain, via the Massif Central to the Eifel, nicely connecting several volcanic regions.

  4. Heellp I’m in the dungeon and there isn’t any cookies .
    I hear gnomes giggling and see a trail of crumbs…

    You’d already been let out by the time I got to you, a lucky escape from those belligerent gnomes… – Admin

  5. The first picture is of Kistufell in Esja, not the Kistufell you’re looking for photos of.

    Kicked out of the spam dungeon for eating cookies – Admin

  6. Could this model of hotspot also explain why the High Lava Plains track and the Snake River Plains hotspot tracks seem to radiate from a central location? I know Team Hotspot and Team Notspot have argued back and forth over that phenomenon for a while now.

    /Released from the home of tasty cookies… Admin!

    • No, the horseshoe shape is from the North American continent changing it’s movement scheme.
      In the beginning the movement was eastish and then took a u-turn and is now moving west-southwest.
      The reason behind this is the spreading of the MAR that slowly started to shuffle the US away from Europé.

    • I can (selfishly) recommend http://www.volcanocafe.org/the-snake-river/

      Hot spot tracks can’t radiate, but convective mantle currents can. But this region is complex. The volcanism is driven as much by the rifting of the US as it is by the Yellowstone hotspot. And the two move in different directions.

      • In all probability the hotspot is locked in Place while the continent does the fandango.

  7. Ah so there we are! Thanks Carl – a great paper. I look forward to the Jan Mayen spinel/garnet research whenever it may happen.

    I look forward also to the potential reawakening of Scottish Volcanism, as ancient as it is. I’ve a vision of a ring of pipers piping up the first vent along with Nicola Sturgeon welcoming the Icelandic free heat source, thumbing her nose at British Nuclear Fuels.

    On the other hand, far more likely absolutely nothing will happen.

  8. Interesting idea. I didn’t like the ‘finger’ model of the recent paper. Two of the ‘fingers’ are just the MAR, and for the others, if you leave the drawn lines off they are not at all obvious. The eye tends to see patterns where there are none. But apart from that, I share your suspicion of the Iceland hot spot. There is some more heat than in a normal mantle, but it is not excessive. If you connect the Iceland hot spot to the lava flows of Greenland, there is a 30 million year gap in activity, and if you connect it to Scotland, the Faroe ridge doesn’t actually connect to Iceland. It seemed to me that those two observations pull the rug from underneath the long-lived hot spot model.

    I am happy to consider a shallow heat source. The one problem with the model of a deepening plume which is breaking the 600 km (and the 400 km) barrier, is that those are broken either by heat from below or by cold above. If you put heat above the layers, they stabilise rather than break. Perhaps what you are seeing is driven by an old, subducted plate below Iceland which is beginning to sink through these layers.

    The Atlantic ocean at Norway seems too young to subduct. It will need another 50 million years before it gets cold enough.

    Perhaps the next instalment of the History of the Earth series should be on the origin of Iceland.

    • It is debatable if Iceland is a real Mantleplume yet. It most likely started as a local mantle upwelling being sucked up by a vortex created by the intricacies of Icelandic plate Tectonics.
      But, I do Think it is a good part on the way to become one since it has burrowed down quite a bit in just 14 million years and there is good evidence that it is both picking up speed and heat as it goes. Even though it is not as warm as Hawaii and The African Superplume it is goodly warm compared to the MORB based lavas at Geirfugladrangur on the Reykjanes Ridge.

      It will definitely take time Before full subduction occurs at Norway, but you allready have a proto-subductive fault, and it is the only reasonable way to explain that there is heating going on under Norway. Currently the bowing is 3km.

      I would love to the the origin of Iceland. But it would be problematic to write since nobody seems to agree with anyone else on how it happened. Sometimes I Think it would be fun to set a date in the future when we do two or more versions of and post it at the same time. I bet you and me would come up with radically different models and that the discussion amongst the readers would be fun 🙂

      • I, for one, would love to see that post-off!

        I have to say I’m not a fan of the micro plate explanation in Iceland. I have a few ideas to explain away it’s existence, maybe something for an article at some point…

  9. Any one take note around Skagway Ak.of all the quakes ?
    quite a swarm. USGS page for west coast NA…:
    https://earthquake.usgs.gov/earthquakes/map/#{“autoUpdate”%3A[“autoUpdate”]%2C”basemap”%3A”grayscale”%2C”feed”%3A”7day_m25″%2C”listFormat”%3A”default”%2C”mapposition”%3A[[44.715513732021336%2C-140.

    • I had a feeling that this article would be needed, but… damn… They just forgot to add the Word murder to it. Giant Murder Spider Plume of Iceland. 🙂

      • Oh come on Carl, it’s ‘Giant murdering cancer-spreading Muslim immigrant Corbyn-loving lefty spider plume of Iceland that threatens to end civilisation in wind-powered death camps’

      • Can’t sleep…
        Quite normal since I am getting up in two hours for the morning flight to South Africa.
        So, instead I am listening to the greatest airplane song of them all, Rush YYZ. YYZ is the calling code for their home Airport, Toronto.

        • I do like a bit of Rush, YYZ is a bass masterpiece, Geddy Lee is a genius. I’m probably biased due to my personal bass playing history… nope I’m definitely biased. Imagine Geddy Lee and Les Claypool jamming together…

        • How about Nazareth – ‘This Flight Tonight’? A truly magmatic masterpiece! Have you got ‘your heat turned on baby’?

  10. I dislike singularities, so let’s find another example! Any fingers under Hawai’i?

      • But, to be fair, there are those with differing opinions.

        Now, we may or may not wind up as fully integrated with “the machine” as put forth in the documentary based on Kurzweil’s book, there are avid self described “Ludites” (such as myself) that doubt if this wholesale adopting of technology will occur. In my opinion, do so will open someone up to much greater scrutiny by entities that wish to exploit this capability. (Feature-Creep) Once you are at that level of integration, you have no recourse at all. One of the underlying plot-lines of Ghost in the Shell uses this as a story mechanism. Is Major Motoko Kutsanagi actually human or is she just an AI manifestation of consciousness. Despite the arguments over Scarlett Johansson playing the role in the upcoming movie, if they stay true to that conflict, then they are true to the storyline. Kutsanagi is a full body cyborg replacement(brain and all), and her nagging question follows that single issue.

        Yes, it’s all fiction, but fiction tends to become predictive with time.

  11. No fingers but since you mentioned my favorite Volcanoes.. I doubt that they would qualify for a mention, unless you were asking. Two deep quakes around Kilauea, one at 45km just north of Ichi Kilauea, and the other at 26km south west of the caldera. We also had another 2.6 at 1.5 km just south west of the Caldera of Mauna loa. They are getting a little closer to the surface with time in the last approx. 15 days going from 3.6km up to 1.5km today in that area.

    Mac

    • The Mauna Loa quake seems to coincide with a slight contraction of the caldera. Perhaps a bit of magma migrated from the summit reservoir to the southwestern rift, shallow enough that the summit no longer sees it.

    • @Macusn

      Ya don’t need fingers. The Hawaiian swell is due to the massive heat flux from the Hawaiian hotspot.

      (searching for this image led me to the paper, which is paywalled, but the abstract is available.)

      Earth and Planetary Science Letters
      Volumes 359–360, 15 December 2012, Pages 40–54

  12. Very intresting Article 🙂 , I am Also beliving Iceland and North Atlantic sits on a larger kind of thermal mantle upwelling? , the relative shallow seas around Iceland and generaly lots flood volcanics in north atlantic and uplifted crust but maybe Thats beacuse that part of the north atlantic is still Young and hot unlike the broader sourthen atlantic? Or maybe I am seeing the remains What the earlier Superplume did there 60 to 55 million years ago and not really any features that haves to do directly with modern day geological activity , still the modern day seafloor crustal structures and thickness / in the North Atlantic is highly suggestive of some kind of deep large plume activity , these features begins where the Azores are and ends a Jan Mayen .. or maybe I am just stumbling and mixing things that does not exist or maybe I am wrong

  13. So just a thought on why the Iceland plume *may* exist.

    Since we know that there are sunken crust slabs sitting somewhere beneath Iceland (likely around 600km deep), here is what I’m possibly thinking.

    1. Assuming there is *any* water in these slabs, the migration of the mid-atlantic ridge could possibly be why we have upwelling in Iceland.

    2. We know that the sunken slabs are likely located around 400-670 km in depth beneath Iceland itself. Normally, water causes melting and percolates out of a sunken slab around 100-120 kilometers in depth. In the past, we would have assumed that there would have been no water in a slab this deep, but somewhat more recently, we have learned that water can be held in a slab way deeper.

    3. I believe around 2014 there were a lot of articles talking about “oceans” of water super-deep in the mantle. These articles were bogus as there were no oceans, but there is something called ringwoodite that is a silicate that traps water inside. I believe this silicate will hold the water in up to around 650km depth (going off memory here, so don’t quote me on this). So normally, this water doesn’t get released, and even if it does, the magma may not make its way up to the surface from that depth.

    4. This is where the MAR enters into the equation. Since the spreading ridge lowers pressure in the mantle below it, I believe this could be the force that influenced the release of water and excess melt in the sunken slabs below Iceland. Basically, as the mid-atlantic ridge migrated into a position such that it was situated above the Iceland sunken slab(s), the pressure gradient was lowered enough that the melt depth of the ringwoodite changed, influencing the release of water from those minerals. This resulted in the excess melting that we see in Iceland.

    Now, I have no clue whether this would be bogus or not, and I’m sure there would be ways we could see if this were the case via magma chemical signatures. But I did think this was a theory worth exploring. Since Iceland isn’t a product of a deep plume, I would believe that the mid-atlantic ridge triggered something in the Mantle to cause excessive magma production.

    • I don’t know what the dehydration characteristics of ringwoodite are. That it looses it’s water at around 670 km has been well published. In the past, I have suggested that the near vertical dangling plates may have an additional melt source from that in locations such as Taal, but I’m not a geochemist and can not say with any certainty that is what happens. That Taal sits over a near vertical hanging slab is evident in the seismic data.

    • There are problems with the timeline here. If the cause was melt arising from these slabs, would the plume not form there and grow upward? The data suggest that the plume formed at the surface and grew downward.

      • No, because it’s not just a factor of melt arising from these slabs. In normal environment, the Ringwoodite does not melt at the depth of 400-600 km deep.

        But when the MAR passed over these slabs, the decreased pressure as a result of normal MAR Rifting made it possible for the Ringwoodite to melt and release water at a depth it wouldn’t normally be capable of. This essentially supercharged the normal volcanism of the mid atlantic ridge, resulting in a big upwelling in that area.

        Just a theory however.

      • The data does not proof th at the plume grew downward. It shows that shallow mantle material reached the surface first. That will happen no matter where the plume forms, as long as it is recent.

  14. …sigh…

    And again. No major threat, other than flooding. (This is normal weather here). It’s actually part of that same overall system from the other day… just a fresh influx of moisture off the Gulf getting picked up by the low in the mid continent.

  15. Shallow earthquake activity underneath an volcanic island in the Aleutian chain which I can’t find the name of. It is one of the Delarof islands, due west of Tanaga Island and north of Ogliuga island. Google only lists it as a wildlife reserve.

      • I’ve emailed AVO and they said it appears to be a normal tectonic swarm at the moment but they’re keeping an eye on it.

        • Thanks for finding this out! The shallowness got my attention, but of course even in volcanic regions most earthquakes are tectonic.

  16. I plotted a cross-section from a tomography model once. It does show the Iceland plume going to around 600km depth or a bit more.

  17. Subduction in the Atlantic. Actually some studies have found what seems to be evidence of an already developing subduction zone off the coast of Portugal. However this process might be still in its early stages. It could also explain the unusual seismicity off the coast of Portugal, including the M8-9 earthquakes that regularly strike the region every few centuries.

    http://news.nationalgeographic.com/news/2013/06/130619-iberia-america-europe-subduction-zone-supercontinents-colliding/
    http://geology.gsapubs.org/content/early/2013/06/05/G34100.1.abstract

  18. I am skeptical of any theory based in very small amount of evidence.

    This recent study is only *one* study, and I am still open for the theory of a hotspot track that originated from the direction of Greenland.

    The finger connection to Scotland makes plenty of sense, in fact many recent studies have shown the widespread influence of “superplumes” at depth that feed individual plumes at shallower levels of the mantle. Examples in Africa and in southwest Pacific. The Icelandic region might show similar behavior and it might be a remain also of an earlier primitive plume that occurred during the breakup of the North Atlantic.

    Meanwhile, off topic, Larsen C ice shelf is about to finish its rifting event and collapse towards the ocean. Its the fourth largest ice shelf in Antartica. Still does not contribute directly to sea level rise. However a bit more south, in the other side of the peninsula, the Pine Island Glacier retreat could be much more of cause for concern, as its retreat and runaway melting could add to up to 0.5m sea level rise.

  19. Another extremely interesting post!! Some questions marks from an amateur. Learnt from Alberts previous posts that subduction actually are the main driving force behind spreading at the MAR, pulling apart the oceanic crust sheets. But were are the subduction driving this going on around the atlantic ocean?? Now we learnt that subduction has initiated along Norway on way under the Scandinavian shield and perhaps along the Portugal coast. When will we see earthquakes along the Norwegian coast? Why not already? Are there subduction zones forming also on the western side of the Atlantic??

    • Well – I don’t see much evidence for subduction near Portugal. The main evidence was the big Lisbon earthquake, as only subduction zones can give an M9. But it turns out this earthquake was nowhere near M9. It was about M8.4, and that is feasible from the known faults there. (The repeat time is a few thousand year, not a few hundred – I have to take the risk of disagreeing with Irpsit on this). I should also say that the South Atlantic is probably closest to developing subduction but it isn’t there yet.

      So where does the pull come from? It comes from the Pacific ocean! The subduction along the west coast of America is pulling Iceland from once side, and the subduction along Asia is pulling at the other side (somewhat hampered by India’s pushing into Asia). Amazing, isn’t it, that the forces act over such larger distances!

      • I think it’s fair to say the Pacific plate is the ‘hub’ of the global tectonic cycle.

      • Thats amazing! The american and euroasian continents are obviously very robust to withstand those forces. Now looking at the subduction zones aroundand in the pacific trying to understand, make a model. Would be interesting with a post on that in the future!

      • I cant see how a subducting plate can “pull” another plate

        I had always thought it was convection in the mantle that caused the movement of plates. Where heat rises up from the inner core and splits each way somewhere around the depths of the moho. And its where this convection currents split off in 2 directions is where you get a spreading zone. The convection drags the crust along with it, and where these crustal plates collide, you either get subduction of one of the plates or collision (such as the Himalayas)

        At least that is how I perceived it looking at pictures in books (I’m not much of reader)

        • This has been a major source of discussion: are plates ‘pulled’ by the subduction zones, or ‘pushed’ by the mantle? I can refer to a post a while ago that discussed this, the dancing earth (http://www.volcanocafe.org/the-dancing-earth-continental-drift/) It is mostly ‘pull’, with a small amount of ‘push’.

          The sinking edge of the plate pulls the rest of its own plate towards it (as you can imagine). And the next plate has to move in to cover the gap, so it affects both plates.

    • They want to look at preserved structures on Venus. Good luck – the planet regularly gets re-surfaced with half a kilometer of lava..

  20. I think one cannot expect full blown subduction to occur already in the Atlantic coast, at the edge of the Eurasia plate.

    I suspect that subduction would start slowly and gradually, with minor earthquakes initially, and a few major ones ocasionally. I would look for patterns of faulting along the coasts of the Eurasian and African plates, in one side, and along the eastern coast of the American continent in the other side.

    At least in the Atlantic side, one can find some interesting things.
    (I am not saying that this is clear evidence but its a clue pointing towards our hypothesis)

    I post the geological faults of Norway. Most faults aligned SW to NE, along the coast. Carl surely knows more about this.

    Geological faults of UK and Ireland. Again most faults aligned SW to NE. Even if accepted knowledge says its nothing to do with subduction I find this interesting.

    Geological faults along the coast of Portugal – information only available in portuguese – but faults are mostly of a vertical movement and aligned SW to NE or S to N.

    The 1755 quake was at least M8.4. And historical evidence (only available in Portuguese) tells of earlier occuring major earthquakes, some with tsunamis, prior to 1755: in the years of 60BC, 382, 1504, 1722 (and possibly also in the years 1009, 1033, 1309, 1356)

    So the fault off the coast of Portugal is regularly producing major tsunamis. The historical data of reported effects shows that such earthquakes are most likely above M8, just like 1755.

    Information for the west coast of Africa is scarse, but obviously we have Holocene volcanism along the coast. I post also the map for Morroco, again faults SW to NE
    https://www.intechopen.com/source/html/37860/media/image1.jpeg

    What I mean to say is that a series of proto-subduction faults may already be developing along the eastern edge of the Atlantic. But as this is still in very early stages, seismicity is only significant off the coast of Portugal. I will look for data in the other side of the Atlantic.

    Askimet found this suspicious. Either that, or tried to censor science. Released from the dungeon – admin

      • Along the eastern side of North America, there are also major geological faults all along the coast (mostly S to N or SW to NE). I don´t know them much well. Subduction is already happening at least in one point of the western side of the Atlantic, in the eastern edge of the Caribbean plate.

        Along Brazil, information is scarse but there are faults along the coast aligned SW-NE

        • I think these faults are mostly left from the opening of the Atlantic, or in the case of the UK northwestern region, the closing of the previous ocean, the Iapetus. But it raises an interesting point: how do you recognize a developing subduction zone? The oceanic crust (only ocean crust subducts: continental crust can’t) must be denser than the mantle below. So you are looking for cold, dense crust which therefore sits very deep.

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