Volcanic Zones of Iceland and the Length of the Flank Zones

The volcanic zones of Iceland replace the Reykjanes Ridge in the south and Kolbeinsey Ridge in the north. This interval, found approximately between 63°N and 67°N, is as complex as the ridges look simple.

The volcanic zones of Iceland.

Here is a list of the zones: A = Snæfellsnes Volcanic Zone B = Reykjanes Peninsula Rift C= Western Volcanic Zone D = Central Iceland Volcanic Zone E = South Iceland Volcanic Zone F = East Volcanic Zone G = North Volcanic Zone H = Öræfajökull Volcanic Zone = I = Grimsey Oblique Rift J = Skagafjordur Volcanic Zone (extict). The red arrows at the bottom indicate mantle convection flow vectors (convective layer 1) just below 120 km depth. Names derived mainly from https://jardvis.hi.is/sites/jardvis.hi.is/files/Pdf_skjol/Jokull58_pdf/jokull58-einarsson.pdf

The drawing is superimposed on a map from the report from National Land Survey of Iceland: https://www.lmi.is/static/files/maelingar/isnlet2004-skyrsla.pdf. The map includes tectonic drift vectors showing shift of position of relevant points was measured with GPS technology within the time interval of 1993-2004.

Here the relationship between individual zones and a relevant pair of convection rolls is considered:

A – Snæfellsnes Volcanic Zone covers a pair of convection rolls, according to the model.

B – Reykjanes Peninsula Obique Rift Zone is not very well defined at its western end, because mapping is terminated at the coastline. It is not a proper geological border, but according to this model the system extends out to the beginning of the regularly aligned Reykjanes Ridge, before it starts bending eastwards towards the peninsula.

C – The Western Volcanic Zone, as defined, extends to the third convection roll in the north, but within that polygon the faults start bending northwards, in the same way as the rifts of D and F.

D – Central Iceland Volcanic Zone is mainly confined to only one polygon, except a part trending slightly west of north. It can be explained according to this model that the convection rolls of second layer affect the surface along the downwelling line.

E – South Iceland Volcanic Zone is itself very divided into the Eyjafjallajökull-Katla part and the Westman Islands part. Those two parts clearly cover a pair of rolls.

F – The East Volcanic Zone spans four polygons. But the central two polygons have a special status, being the only two clearly belonging to it. The southernmost polygon is divided into two parts, as a transition over to the South Iceland VZ (marked E). The northernmost polygon plays the role of transition over to the North Volcanic Zone, and has similar features as the polygon of the West Volcanic Zone at the same latitude.

G – The North Volcanic Zone, as defined here, extends over a pair of convection rolls, of convective layers 3 and 4. If we would define the NVZ as extending farther south (to Kverkfjöll Volcano), the zone would be seen covering two rolls of layer 1 and 2. A question of definition is met at the northern end, because it is submerged and not as clearly mapped as other parts.

H – Öræfajökull Volcanic Zone is a flank zone, clearly extending over a pair of convection rolls of the 4th layer, that is closest to the 410 km discontinuity.

I – The Grímsey Oblique Rift Volcanic Zone is hardly ever mentioned as a volcanic zone, because it is found under the ocean. Geologically, it has similar properties as the Reykjanes Peninsula. The upper most convection rolls below 120 km depth are found to mark the ends of this zone.

J – The extinct volcanic zone of Skagafjordur is most often omitted on simplified geological maps. The last eruption took place there less than 800.000 years ago, so the main features of Iceland were the same as today. The area is still geothermally active. Therefore, I tend to include this as a volcanic zone, specially because some rifting took place making Skagafjordur wider (perhaps 10 km wider) during a million years period of rifting process. https://orkustofnun.is/gogn/Greinar-starfsmanna/Arni-Hjartarson-2003-PhD/AH-04-Skagafjordur-Zone-an-ephemeral-Rift-Zone.pdf. The zone also seems to have covered a pair of convection rolls, of layer 4.

The volcanic zones, seem to fit quite well into sections of pairs of volcanic rolls. The model might therefore prove useful for a more accurate mapping and definitions of the outer limits of the zones, besides combining in the south with the Central Iceland VZ (D).

The four convective layers mentioned are found in between 120 and 410 km depth, the uppermost one labelled as convection layer 1.

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