Bulletin of Volcanology

, 75:764 | Cite as

Structure of regional dykes and local cone sheets in the Midhyrna-Lysuskard area, Snaefellsnes Peninsula (NW Iceland)

  • Alessandro Tibaldi
  • Fabio Luca Bonali
  • Federico Aligi Pasquaré
  • Derek Rust
  • Alessandro Cavallo
  • Alessandro D’Urso
Research Article


This paper provides the first detailed structural description of 48 vertical dykes, 384 inclined sheets and two large intrusions and the geometry (strike, dip direction and dip) of 1116 fractures in the central area of the Snaefellsnes peninsula, NW Iceland. Our data show a more complex setting than that depicted by the WNW-ESE en-echelon trend of the volcanic structures at the surface. In the Miocene basement lavas, dykes dominantly strike N50–100°E whereas other directions are also present with a higher dispersion. Two main swarms of centrally dipping sheets have also been recognized, focussing towards two areas. Sheet dips range from 2 to 75° with the higher frequency between 10 and 45°. In section view, there is no systematic variation of sheet dip with distance from the focus area. Gabbro and granophyre laccoliths are present in the studied area but cross-cutting relations indicate that most of the inclined sheets are younger. Comparison with regional tectonics suggests that the N50–80°E-striking dykes are coherent with emplacement under the stress field of the pre-6 Ma Snaefellsnes Rift dominated by a NNW-SSE-directed least principal stress (σ3). The N80–100°E dykes and the late Quaternary WNW-trending sub-aerial volcanic features are instead consistent with the development of a more recent E-W, right-lateral shear zone affecting the Snaefellsnes peninsula. Coherent sets of fractures have also been found. Within the inclined sheet swarms, the stress tensor rotated in response to an excess magma pressure linked to two underlying magma chambers of lobate shape, located at an estimated depth of about 400 and 500 m below sea level. This local magmatic stress also produced the centrally inclined fracture swarms that have been found in this area.


Iceland Snaefellsnes Dyke Inclined sheet Tectonics Magma chamber 



This is a contribution to the International Lithosphere Program Task Force II “Volcanoes and society: environment, health and hazards”. The Authors are grateful to Andrea Villan, Luca Corti and Luca Fumagalli for field cooperation. Claudia Corazzato is acknowledged for her insights and comments to the 3D structural model. Agust Gudmundsson and an anonymous reviewer are acknowledged for their insightful comments and suggestions to the previous version of the manuscript.


  1. Acocella V, Neri M (2009) Dike propagation in volcanic edifices: overview and possible developments. Tectonophysics 471:67–77CrossRefGoogle Scholar
  2. Ancochea E, Brandle JL, Huertas MJ, Cubas CR, Hernan F (2003) The felsic dikes of La Gomera (Canary Islands): identification of cone-sheet and radial dyke swarms. J Volcanol Geotherm Res 120:197–206CrossRefGoogle Scholar
  3. Bailey EB, Clough CT, Wright WB, Richey JE, Wilson GV (1924) The Tertiary and post-Tertiary geology of Mull, Loch Aline and Oban. Geological Survey of Scotland Memoir, 445 pGoogle Scholar
  4. Bald N, Noe-Nygaard A, Pedersen K (1971) The Kroksfjordur central volcano in North-West Iceland. Acta Naturalia Islandica, II, 10, 29 pages.Google Scholar
  5. Bistacchi A, Tibaldi A, Pasquarè FA, Rust D (2012) The association of cone-sheets and radial dykes: data from the Isle of Skye (UK), numerical modelling, and implications for shallow magma chambers. Earth Planet Sci Lett 339–340:46–56CrossRefGoogle Scholar
  6. Bonali FL, Corazzato C, Tibaldi A (2011) Identifying rift zones on volcanoes: an example from La Réunion Island. Indian Ocean B Volcanol 73(3):347–366. doi: 10.1007/s00445-010-0416-1 CrossRefGoogle Scholar
  7. Brown GC, Everett SP, Rymer H, McGarvie DW, Foster I (1991) New light on caldera evolution—Askja, Iceland. Geology 19:352–355CrossRefGoogle Scholar
  8. Burchardt S, Tanner DC, Troll VR, Krumbholz M, Gustafsson LE (2011) Three-dimensional geometry of concentric intrusive sheet swarms in the Geitafell and the Dyrfjöll volcanoes, eastern Iceland. Geochemy Geophy Geosy 12:Q0AB09, doi:  10.1029/2011GC003527.
  9. Chadwick WW Jr, Dieterich JH (1995) Mechanical modelling of circumferential and radial dike intrusion on Galapagos volcanoes. J Volcanol Geotherm Res 66:37–52CrossRefGoogle Scholar
  10. Corazzato C, Tibaldi A (2006) Fracture control on type, morphology and distribution of parasitic volcanic cones: An example from Mt. Etna, Italy. J Volcanol Geotherm 823 Res 158(1–2):177–194Google Scholar
  11. Cox KG, Bell JD, Pankhurst RJ (1979) The interpretation of igneous rocks. George Allen and Unwin, LondonCrossRefGoogle Scholar
  12. Einarsson P (2008) Plate boundaries, rifts and transforms in Iceland. Jökull 58:35–58Google Scholar
  13. Einarsson P, Brandsdottir B (1980) Seismological evidence for lateral magma intrusion during the July 1978 deflation of the Krafla volcano in NE Iceland. J Geophys 47:160–165Google Scholar
  14. Einarsson P, Brandsdottir B, Gudmundsson MT, Bjornsson H, Gronvold K, Sigmundsson F (1997) Center of the Iceland hotspot experiences volcanic unrest, Eos Trans. AGU 78:369374–369375Google Scholar
  15. Flude S, Burgess R, McGarvie DW (2008) Silicic volcanism at Ljósufjöll, Iceland: insights into evolution and eruptive history from Ar–Ar dating. J Volcanol Geotherm 169(3–4):154–175Google Scholar
  16. Fridleifsson IB (1977) Distribution of large basaltic intrusions in the Icelandic crust and the nature of the layer 2–layer 3 boundary. Geol Socam Bull 11:1689–1693Google Scholar
  17. Galland O, Planke S, Neumann E-R, Malthe-Sørenssen A (2009) Experimental modelling of shallow magma emplacement: application to saucer-shaped intrusions. Earth Planet Sci Lett 277:373–383CrossRefGoogle Scholar
  18. Gautneb H, Gudmundsson A (1992) Effect of local and regional stress fields on sheet emplacement in West Iceland. J Volcanol Geotherm Res 51:339–356CrossRefGoogle Scholar
  19. Gautneb H, Gudmundsson A, Oskarsson N (1989) Structure, petrochemistry, and evolution of a sheet swarm in an Icelandic central volcano. Geol Mag 126:659–673CrossRefGoogle Scholar
  20. Geikie A (1897) The ancient volcanoes of Great Britain. Macmillan, LondonGoogle Scholar
  21. Geshi N (2005) Structural development of dike swarms controlled by the change of magma supply rate: the cone sheets and parallel dike swarms of the Miocene Otoge igneous complex, Central Japan. J Volcanol Geotherm Res 141:267–281CrossRefGoogle Scholar
  22. Gianelli G (1972) Cumulus textures of the Midhyrna layered intrusion, Snaefellsnes Peninsula, western Iceland. Boll Soc Geol Ital 91:419–438Google Scholar
  23. Gudmundsson A (1990) Emplacement of dikes, sills and crustal magma chambers at divergent plate boundaries. Tectonophysics 176(3–4):257–275Google Scholar
  24. Gudmundsson A (1995) Infrastructure and mechanics of volcanic systems in Iceland. J Volcanol Geotherm Res 64:1–22CrossRefGoogle Scholar
  25. Gudmundsson MT (1997) Gravity and magnetic studies of the subglacial Grímsvötn volcano, Iceland: implications for crustal and thermal structure. J Geophys Res 102(B4):7691–7704CrossRefGoogle Scholar
  26. Gudmundsson A (1998) Magma chambers modeled as cavities explain the formation of rift zone central volcanoes and their eruption and intrusion statistics. J Geophys Res 103(B4):7401–7412CrossRefGoogle Scholar
  27. Gudnmundsson A (2000) Dynamics of volcanic systems in Iceland: example of tectonism and volcanism at juxtaposed hot spot and mid-ocean ridge systems. Annu Rev Earth Planet Sci 28:107–140CrossRefGoogle Scholar
  28. Gudmundsson A (2002) Emplacement and arrest of sheets and dikes in central volcanoes. J Volcanol Geotherm Res 116:279–298CrossRefGoogle Scholar
  29. Gudmundsson A (2006) How local stresses control magma-chamber ruptures, dyke injections, and eruptions in composite volcanoes. Earth-Sci Rev 79:1–31CrossRefGoogle Scholar
  30. Gudmundsson A, Brenner SL (2004) How mechanical layering affects local stresses, unrests, and eruptions of volcanoes. Geophys Res Lett 31(16):L16606Google Scholar
  31. Gudmundsson A., Brenner SL (2005) On the conditions of sheet injections and eruptions in stratovolcanoes. Bull Volcanol 67:768–782Google Scholar
  32. Gudmundsson A, Bergerat F, Angelier J (1996) Off-rift and rift-zone palaeostresses in Northwest Iceland. Tectonophysics 255:211–228CrossRefGoogle Scholar
  33. Jacoby W, Gudmundsson MT (2007) Hotspot Iceland: an introduction. J Geodyn 43(1):1–5Google Scholar
  34. Jakobsdóttir SS, Roberts MJ, Gudmundsson GB, Geirsson H, Slunga R (2008) Earthquake swarms at Upptyppingar, north-east Iceland: a sign of magma intrusion? Stud Geophys Geod 52(4):513–528Google Scholar
  35. Jóhannesson H (1980) Stratigraphy and the development of rift zones in West Iceland. Náttúrufrædingurinn 50:13–31 (in Icelandic)Google Scholar
  36. Johnson SE, Paterson SR, Tate MC (1999) Structure and emplacement history of a multiple-center. cone-sheet-bearing ring complex: the Zarza intrusive complex, Baja California, Mexico. Geol Soc Am Bull 111(4):607–619CrossRefGoogle Scholar
  37. Kjartansson G (1968) Geological Map of Iceland. Sheet 2. Icelandic Museum of Natural History and Iceland Geodetic Survey, Reykjavik, scale 1:250,000.Google Scholar
  38. Klausen MB (2004) Geometry and mode of emplacement of the Thverartindur cone sheet swarm, SE Iceland. J Volcanol Geotherm Res 138:185–204CrossRefGoogle Scholar
  39. Klausen MB (2006) Geometry and mode of emplacement of dike swarms around the Birnudalstindur igneous centre, SE Iceland. J Volcanol Geotherm Res 151(4):340–356CrossRefGoogle Scholar
  40. Kristjánsson L, Jónsson G (1998) Aeromagnetic results and the presence of an extinct rift zone in western Iceland. J Geodyn 25(1–2):99–108Google Scholar
  41. Magee C, Stevenson C, O’Driscoll B, Schofield N, McDermott K (2012) An alternative emplacement model for the classic Ardnamurchan cone sheet swarm, NW Scotland, involving lateral magma supply via regional dykes. J Struct Geol 43:73–91CrossRefGoogle Scholar
  42. Martin E, Sigmarsson O (2010) Thirteen million years of silicic magma production in Iceland: links between petrogenesis and tectonic settings. Lithos 116:129–144CrossRefGoogle Scholar
  43. Mathieu L, van Wyk de Vries B, Holohan EP, Troll VR (2008) Dykes, cups, saucers and sills: analogue experiments on magma intrusion into brittle rocks. Earth Planet Sci Lett 271:1–13CrossRefGoogle Scholar
  44. Mjelde R, Raum T, Breivik AJ, Faleide JI (2008) Crustal transect across the North Atlantic. Mar Geophys Res 29:73–87Google Scholar
  45. Moorbath S, Sigurdsson H, Goodwin R (1968) K-R ages of the oldest exposed rocks in Iceland. Earth Planet Sci Lett 4(3):197–205CrossRefGoogle Scholar
  46. Paquet F, Dauteuil O, Hallot E, Moreau F (2007) Tectonics and magma dynamics coupling in a dyke swarm of Iceland. J Struct Geol 29:1477–1493CrossRefGoogle Scholar
  47. Pasquarè F, Tibaldi A (2007) Structure of a sheet-laccolith system revealing the interplay between tectonic and magma stresses at Stardalur Volcano, Iceland. J Volcanol Geotherm Res 161(1–2):131–150CrossRefGoogle Scholar
  48. Phillips WJ (1974) The dynamic emplacement of cone sheets. Tectonophysics 24:69–84CrossRefGoogle Scholar
  49. Saemundsson K (1979) Outline of the geology of Iceland. Jokull 29:7–28Google Scholar
  50. Schilling JG (1973) Iceland Mantle Plume: Geochemical Study of Reykjanes Ridge. Nature 242(5400):565–571Google Scholar
  51. Schirnick C, van den Bogaard P, Schmincke H-U (1999) Cone sheet formation and intrusive growth of an oceanic island—the Miocene Tejeda complex on Gran Canaria (Canary Islands). Geology 27(3):207–210CrossRefGoogle Scholar
  52. Sigmundsson F, Schmundsson K (2008) Iceland: a window on North-Atlantic divergent plate tectonics and geologic processes. Episodes 31(1):92–97Google Scholar
  53. Sigurdsson H (1970) Structural origin and plate tectonics of the Snaefellsnes volcanic zone, Western Iceland. Earth Planet Sci Lett 10:129–135CrossRefGoogle Scholar
  54. Siler DL, Karson JA (2009) Three-dimensional structure of inclined sheet swarms: implications for crustal thickening and subsidence in the volcanic rift zones of Iceland. J Volcanol Geotherm Res 18(8):333–346CrossRefGoogle Scholar
  55. Steinthorsson S (1967) Tvær nýjar C14 aldurákvardanir á öskulögum úr Snæfellsjökli (Two new C14 dates on tephra layers from Snæfellsjökull). NáttúrufræðingurinnGoogle Scholar
  56. Sturkell E, Einarsson P, Sigmundsson F, Hreinsdóttir S, Geirsson H (2003) Deformation of Grímsvötn volcano, Iceland: 1998 eruption and subsequent inflation. Geophys Res Lett 30:B4CrossRefGoogle Scholar
  57. Sturkell E, Einarsson P, Roberts MJ, Geirsson H, Gudmundsson MT, Sigmundsson F, Pinel V, Gudmundsson GB, Ólafsson H, Stefánsson R (2008) Seismic and geodetic insights into magma accumulation at Katla subglacial volcano, Iceland: 1999 to 2005. J Geophys Res 113:B3CrossRefGoogle Scholar
  58. Tchalenko JS (1970) Similarities between shear zones of different magnitudes. Geol Soc Am Bull 81(6):1625–1640CrossRefGoogle Scholar
  59. Tentler T, Temperley S (2007) Magmatic fissures and their systems in Iceland: a tectonomagmatic model. Tectonics 26, TC5019. doi: 10.1029/2006TC002037 Google Scholar
  60. Thordarson T, Hoskuldsson A (2002) Classic Geology in Europe. Monograph, VIII, pp 200Google Scholar
  61. Tibaldi A (1995) Morphology of pyroclastic cones and tectonics. J Geophys Res 100(12):24521–24535Google Scholar
  62. Tibaldi A, Romero JL (2000) Morphometry of Late Pleistocene–Holocene faulting in the southern Andes of Colombia and volcano-tectonic relationships. Tectonics 19(2):358–377CrossRefGoogle Scholar
  63. Tibaldi A, Pasquarè FA (2008) A new mode of inner volcano growth: the “flower intrusive structure”. Earth Planet Sci Lett 271:202–208CrossRefGoogle Scholar
  64. Tibaldi A, Pasquarè FA, Tormey D (2010) Volcanism in reverse and strike-slip fault settings. In: New frontiers in integrated solid earth sciences, Editors: Cloetingh S, Negendank J, Springer, New York, 315–348. doi:  10.1007/978-90-481-2737-5
  65. Tibaldi A, Pasquarè AF, Rust D (2011) New insights into the cone sheet structure of the Cuillin Complex, Isle of Skye, Scotland. J Geol Soc Lond 168:689–704CrossRefGoogle Scholar
  66. Upton BGJ, Wright JB (1961) Intrusions of gabbro and granophire in the Snaefelsness, western Iceland. Geol Mag 98(6):488–492CrossRefGoogle Scholar
  67. Walker GPL (1958) Geology of the Reydarfjordur Area, Eastern Iceland. Q J Geol Soc 114(1/4):367–391CrossRefGoogle Scholar
  68. Walker GPL (1960) Zeolite zones and dike distribution in relation to the structure of the basalts of eastern Iceland. J Geol 68:515–528CrossRefGoogle Scholar
  69. Walker GPL (1974) The structure of Eastern Iceland. In: Kristjánsson L (ed) Geodynamics of Iceland and the North Atlantic Area. Reidel, Dordrecht, pp 177–188Google Scholar
  70. Walker GPL (1975) Intrusive sheet swarms and the identity of Crustal Layer 3 in Iceland. J Geol Soc Lond 131:143–161CrossRefGoogle Scholar
  71. Walker GPL (1992) “Coherent intrusion complexes” in large basaltic volcanoes — a new structural model. J Volcanol Geotherm 50(1–2):41–54Google Scholar
  72. Walker GPL (1999) Volcanic rift zones and their intrusion swarms. J Volcanol Geotherm 94(1–4):21–34Google Scholar
  73. Welke H, Moorbath S, Cumming GL, Sigurdsson H (1968) Lead isotope studies on igneous rocks from Iceland. Earth Planet Sci Lett 4(3):221–231CrossRefGoogle Scholar
  74. Wilson M (1989) Igneous petrogenesis. Unwin Hyman, LondonCrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Alessandro Tibaldi
    • 1
  • Fabio Luca Bonali
    • 1
  • Federico Aligi Pasquaré
    • 2
  • Derek Rust
    • 3
  • Alessandro Cavallo
    • 1
  • Alessandro D’Urso
    • 1
  1. 1.Department of Earth and Environmental SciencesUniversity of Milan-BicoccaMilanItaly
  2. 2.Department of Theoretical and Applied SciencesInsubria UniversityVareseItaly
  3. 3.Centre for Applied Geoscience, School of Earth and Environmental SciencesUniversity of PortsmouthPortsmouthUK

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