Hostname: page-component-76fb5796d-r6qrq Total loading time: 0 Render date: 2024-04-25T15:33:13.867Z Has data issue: false hasContentIssue false
  • English
  • Français

Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano

Published online by Cambridge University Press:  01 May 2009

Håvard Gautneb ,
Agust Gudmundsson  and
Niels Oskarsson
Håvard Gautneb
Affiliation:
Nordic Volcanological Institute, University of Iceland, 101 Reykjavik, Iceland
Agust Gudmundsson
Affiliation:
Nordic Volcanological Institute, University of Iceland, 101 Reykjavik, Iceland
Niels Oskarsson
Affiliation:
Nordic Volcanological Institute, University of Iceland, 101 Reykjavik, Iceland
Get access Rights & Permissions [Opens in a new window]

Abstract

Strike, dip, and thickness were measured for 504 sheets (inclined sheets and dykes) in the 4–6 Ma old Hafnarfjall central volcano in southwest Iceland. The average dip of sheets is 65°, 80% are less than 1.2 m thick, and the thickness tends to decrease with decreasing dip. In 0.5 km long traverses perpendicular to the average strike of sheets, the percentage of sheets ranges from about 6 to 11.

Of 140 chemically analysed sheets most are quartz-tholeiites; a few are intermediate or acid. The sheets are chemically more evolved than the host rock and were generated by a shallow crustal magma chamber at a mature stage of the central volcano, whereas the host rock was generated earlier before the chamber was established. Trace element results suggest that the sheet magmas evolved by low-pressure fractional crystallization as well as by mixing of primitive magmas and crustal melts.

A model is proposed where most of the sheets are generated by a growing shallow magma chamber. As the chamber grows its shape changes, and so does the local stress field associated with it. Because the sheets follow the stress trajectories of the local stress field, the potential pathways of the sheets change with the growth of the chamber, which may explain the common occurrence of cross-cutting sheets. From the evolved chemistry of the sheets, as well as from the pattern of the stress trajectories, it is concluded that the bulk of the sheets were injected from the upper part of the shallow magma chamber.

Type
Articles
Information
Geological Magazine , Volume 126 , Issue 6 , November 1989 , pp. 659 - 673
Copyright
Copyright © Cambridge University Press 1989

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Anderson, E. M. 1936. The dynamics of the formation of cone sheets, ring-dykes and caldron subsidences. Proceedings of the Royal Society of Edinburgh 56, 128–57.Google Scholar
Bailey, E. B., Clough, C. T., Wright, W. B., Richey, J. E. & Wilson, G. V. 1924. Tertiary and post-Tertiary geology of Mull, Loch Aline and Oban. Scotland Geological Survey Memoirs. 441 pp.Google Scholar
Billings, M. P. 1972. Structural Geology. Englewood Cliffs, New Jersey: Prentice-Hall. 606 pp.Google Scholar
Carmichael, I. S. E. 1964. The petrology of the Thingmuli, a Tertiary volcano in eastern Iceland. Journal of Petrology 5, 435–60.Google Scholar
Gerlach, T. M. 1986. Exsolution of H2O, CO2, and S during eruptive episodes at Kilauea volcano, Hawaii. Journal of Geophysical Research 91, 12177–85.Google Scholar
Gibson, I. L., Kirkpatrick, R. J., Emmerman, R., Schmincke, H-U., Pritchard, G., Oakley, P. J., Thorpe, R. S. & Marriner, G. F. 1982. The trace element composition of the lavas and dikes from a 3-km vertical section through the lava pile of eastern Iceland. Journal of Geophysical Research 87, 6532–46.Google Scholar
Gudmundsson, A. 1983. Form and dimensions of dykes in eastern Iceland. Tectonophysics 95, 295–307.Google Scholar
Gudmundsson, A. 1984. Formation of dykes, feeder-dykes and the intrusion of dykes from magma chambers. Bulletin Volcanologique 47, 537–50.Google Scholar
Gudmundsson, A. 1986. Formation of crustal magma chambers in Iceland. Geology 14, 164–6.Google Scholar
Gudmundsson, A. 1987 a. Formation and mechanics of magma reservoirs in Iceland. Geophysical Journal of the Royal Astronomical Society 91, 27–41.Google Scholar
Gudmundsson, A. 1987 b. Lateral magma flow, caldera collapse, and a mechanism of large eruptions in Iceland. Journal of Volcanology and Geothermal Research 34, 65–78.Google Scholar
Gudmundsson, A. 1988. Formation of collapse calderas. Geology 16, 808–10.Google Scholar
Harker, A. 1904. The Tertiary Igneous Rocks of Skye. U.K. Geological Survey Memoir, 481 pp.Google Scholar
Hills, S. E. 1972. Elements of Structural Geology. London: Chapman and Hall. 502 pp.Google Scholar
Jakobsson, S. P. 1972. Chemistry and distribution pattern of recent basaltic rocks in Iceland. Lithos 5, 365–86.Google Scholar
Jakobsson, S. P. 1979. Outline of the petrology of Iceland. Jokull 29, 57–73.Google Scholar
Jaeger, J. C. 1964. Thermal effects of intrusions. Review of Geophysics 2, 443–6.Google Scholar
Lekhnitskii, S. G. 1968. Anisotropic Plates. New York: Gordon & Breach Science Publishers. 534 pp.Google Scholar
Mindlin, R. D. & Cheng, D. H. 1950. Nuclei of strain in the semi-infinite solid. Journal of Applied Physics 21, 926–30.Google Scholar
O'Hara, M. J. 1977. Geochemical evolution during fractional crystallization of a periodically refilled magma chamber. Nature 266, 503–7.Google Scholar
Oskarsson, N., Sigvaldasson, G. E. & Steinthorsson, S. 1982. A dynamic model of riftzone petrogenesis and the regional petrology of Iceland. Journal of Petrology 23, 28–74.Google Scholar
Palmason, G. 1971. The crustal structure of Iceland from explosion seismology. Visindafelag Islendinga Greinar 40, 1–187.Google Scholar
Pearce, J. & Norry, M. J. 1979. Petrogenetic implications of Ti, Zr, Y and Nb variations in volcanic rocks. Contributions to Mineralogy and Petrology 69, 33–47.Google Scholar
Phillips, W. J. 1974. The dynamic emplacement of cone sheets. Tectonophysics 24, 69–84.Google Scholar
Robson, G. R. & Barr, K. G. 1964. The effect of stress on faulting and minor intrusions in the vicinity of a magma body. Bulletin Volcanologique 27, 315–30.Google Scholar
Ryan, M. P. 1987. Neutral buoyancy and the mechanical evolution of magmatic systems. In Magmatic Processes: Physiochemical Principles (ed. Mysen, B. O.), pp. 259–87. Pennsylvania State University, Geochemical Society Special Publication No. 1.Google Scholar
Saemundsson, K. 1979. Outline of the geology of Iceland. Jokull 29, 7–28.Google Scholar
Savin, G. N. 1961. Stress Concentration Around Holes, New York: Pergamon Press. 430 pp.Google Scholar
Sigurdsson, H. 1966. Geology of the Setberg area, Snaefellsnes, western Iceland. Visinidafelag Islendinga Greinar 4 (no. 2), 53–125.Google Scholar
Smith, J. V. 1974. Feldspar Minerals, Vol. 2. Berlin: Springer Verlag. 685 pp.Google Scholar
Sneddon, I. N. 1951. Fourier Transforms. New York: McGraw-Hill. 542 pp.Google Scholar
Tsuchida, E. & Nakahara, I. 1970. Three-dimensional stress concentration around a spherical cavity in a semi-infinite elastic body. Bulletin of the Japan Society of Mechanical Engineers 13, 499–508.Google Scholar
Tsuchida, E. & Nakahara, I. 1974. Stress concentration around a spherical cavity in a semi-infinite elastic body under uniaxial tension. Bulletin of the Japan Society of Mechanical Engineers 17, 1207–17.Google Scholar
Walker, G. P. L. 1974. The structure of eastern Iceland. In Geodynamics of Iceland and the North Atlantic Area (ed. Kristjansson, L.), pp. 177–88. Dordrecht: Reidel.Google Scholar
Walker, G. P. L. 1975. Intrusive sheets swarms and the identity of crustal layer 3 in Iceland. Journal of the Geological Society of London 131, 143–61.Google Scholar
Williams, H. & McBirney, A. R. 1979. Volcanology. San Francisco: Freeman, Cooper & Company. 397 pp.Google Scholar
Wood, D. A., Gibson, I. L. & Thompson, R. N. 1976. Elemental mobility during zeolite facies metamorphism of the Tertiary basalts of eastern Iceland. Contributions to Mineralogy and Petrology 55, 241–54.Google Scholar