Geology

Geology

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The Iceland basalt plateau is situated at the junction of two large submarine physiographic structures, the Mid-Atlantic Ridge and the Greenland–Iceland–Faeroe Ridge.
The plate boundary is where active spreading and plate growth take place. It can be viewed as a structure where the crust is being pulled apart and molten rock wells up to fill the gash. This plate boundary is delineated by series of faults and volcanoes, which together form a distinguishing ridge – like structure (Thordarson et al., 2002).

Current distribution and arrangement of active volcanism in Iceland results from superposition of the spreading plate boundary over the Iceland mantle plume as well as the relative motion of these two structures. The surface expressions of this interaction are the neovolcanic zones; a discrete 15–50 km wide belts of active faulting and volcanism. There are five active volcanic systems within the 70km wide and 200km long North Volcanic Zone
(Thordarson et al., 2002).


Geological situation Iceland (Thordarson et al., 2002)

The volcanic system can be viewed as the principal geological structure in Iceland. It is characterized by conspicous volcanotectonic architecture that features a fissure (dyke) swarm or a central volcano or both and has a typical lifetime of 0.5–1.5 million years. The fissure swarms of each system are elongate structures that normally are aligned sub-parallel to the axis of the hosting volcanic zone. The central volcano, when present, is the focal point of eruptive activity and typically the largest edifice within each system. The cluster of volcanic and tectonic surface structures are now used to define the volcanic systems (Thordarson et al., 2002).

 

1. Reykjanes

2. Krýsuvík

3. Brennisteinsfjöll

4. Hengill,

5. Hróðmundartindur

6. Grímsnes

7. Hrafnabjörg

8. Prestahnjúkur

9. Kjölur

10. Hofsjökull

11. Kerlingarfjöll

12. Tungnafellsjökull

13, Vestmannaeyjar

14. Eyjafjallajökull

15. Katla

16. Tindfjöll,

 

17. Hekla

18. Torfajökull

19, Veiðivötn

20. Grímsvötn

21. Kverkfjöll

22. Askja

23. Fremrinámur

24. Krafla

25. Þeystareykir

26. Öræfajökull

27. Esjufjöll

28. Snæfell

29. Ljósufjöll

30. Helgrindur

31. Snæfellsjökull

 

 

Distribution and components of active volcanic systems in Iceland (Thordarson et al., 2002)

The main feature of NE Iceland is the North Volcanic Zone and the Tjörnes Fracture Zone:

North volcanic zone

The North (NVZ) Volcanic Zone, and also the West (WVZ) Volcanic Zone, are typified by tholeiitic magmatism and theye are joined by Mid-Iceland Belt (MIB) and are linked to the Mid-Atlantic Ridge system by the Reykjanes Volcanic Zone (RVZ) in the south and the Tjörnes Fracture Zone (TFZ) in the North. The key consquences of rift jumps in the North Volcanic Zone are the trapping of older crust between the two rift segments (Thordarson et al., 2002).

Tjörnes Fracture Zone

It is a broad zone of seismicity, transform faulting and crustal extension that connects the southern end of the submarine Kolbeinsey Ridge to the volcanic rift zone in North Iceland. The transform motion appears to be taken up by several parallel NW-striking seismic zones. The northernmost one, the Grímsey zone, which is entirely off shore, has an overall NW-SE trend but N-S structural elements are also prominent. A series of graben-like troughs with this trend have been identified, indicating crustal dilation. The Grímsey zone joins the Northern Volcanic Rift Zone in the Axarfjörður Bay, where it merges with the Krafla fissure swarm.
A second seismic zone is about 40 km south of the first one, and is well defined by the seismicity near its western end, near the mouth of Eyjafjörður. The fault zone can be traced on the ocean bottom to the coast in the Húsavík town, continuing on land into the Northern Volcanic Zone, where it merges into the Theistareykir fissure swarm. A common feature is the occurrence of earthquakes on transverse structures (Einarsson, 1991a).


Epicenters of earthquakes in North Iceland 1981 - 1986 (Einarsson, 1991a)

In the east of Iceland there is also an active intraplate volcanic belt. Young volcanic rocks ( less than 2 Mio years old) rest unconformably on older formations. The Öræfi Volcanic Belt (ÖVB) is situated to the east of the plume centre and the current plate margins and presents an embryonic rift. This Volcanic Belt shows a possible move of entire Iceland to the west and indicate therefor another jump in the spreadingaxis across Iceland (Thordarson et al., 2002).