Jökull - 01.12.2006, Síða 75

Pleistocene rhyolitic volcanism at Torfajökull, Iceland
ÁGRIP
Nýlegar argon-argon aldursgreiningar á súru bergi af
Torfajökulssvæðinu gefa aldur á bilinu 67-384 millj-
ónir ára. Efnagreiningar á aðalefnum og snefilefnum
sýna ennfremur að elsta bergið er mest þróað, sem
gefur til kynna að Torfajökulseldstöðin hafi verið virk
í a.m.k. 400 þúsund ár. Stærstu þekktu gosin á svæð-
inu, Rauðfossafjöll og Illihnúkur, urðu á síðustu ísöld,
fyrir um 70 þúsund árum. Súrir stapar gefa hugmynd
um ísþykkt jökulhettunnar á myndunartíma. Yngri
gos eru öll mun minni og blönduð basískri kviku sem
gæti bent til aukinna áhrifa gliðnunar eftir ísöld.
REFERENCES
Anderson, A. T. 1984. Probable relations between plagio-
clase zoning and magma dynamics, Fuego Volcano,
Guatemala. Am. Mineral. 69, 660–676.
Barberi, F., G. Ferrara, R. Santacroce, M. Treuil and J.
Varet 1975. A transitional basalt-pantellerite sequence
of fractional crystallisation, the Boina Centre (Afar,
Ethiopia). J. Petrology 16, 22–56.
Björnsson, H. 1988. Hydrology of ice caps in volcanic re-
gions. Soc. Sci. Isl. 45, 1–139.
Blake, S. 1984. Magma mixing and hybridisation pro-
cesses at the alkalic, silicic, Torfajökull central vol-
cano triggered by tholeiitic Veiðivötn fissuring, south
Iceland. J. Volcanol. Geotherm. Res. 22, 1–31.
Carmichael, I. S. E. 1964. The petrology of Thingmuli,
a Tertiary volcano in Eastern Iceland. J. Petrology 5,
435–460.
Davies, G.R. and R. Macdonald 1987. Crustal influences
in the petrogenesis of the Naivasha basalt-comendite
complex: combined trace element and Sr-Nd-Pb iso-
tope constraints. J. Petrology 28, 1009–1031.
Edwards, B.R., J.K. Russell and R.G. Anderson 2002.
Subglacial, phonolitic volcanism at Hoodoo Mountain
volcano, northern Canadian Cordillera. Bull. Volcanol.
64, 254–272.
Friðleifsson, G. Ó. and K. Sæmundsson 2001. Hydrother-
mal map of the Torfajökull central volcano, 1:40,000.
National Energy Authority, Iceland.
Guðmundsson, M. T., F. Sigmundsson, H. Björnsson and
Þ. Högnadóttir 2004. The 1996 eruption at Gjálp,
Vatnajökull ice cap: efficiency of heat transfer, ice
deformation and subglacial water pressure. Bull. Vol-
canol. 66, 46–65.
Guðmundsson, M.T. 2005. Subglacial volcanic activity in
Iceland. In: Iceland – Modern Processes and Past En-
vironments, Caseldine C., A. Russell, J. Harðardottir
and O. Knudsen (eds.), Elsevier, 127–151.
Gunnarsson, B., B. D. Marsh and H. P. Taylor Jr.
1998. Generation of Icelandic rhyolites: silicic lavas
from the Torfajökull central volcano. J. Volcanol.
Geotherm. Res. 83, 1–45.
Haflidason, H., J. Eiriksson and S. Van Krefeld 2000. The
tephrochronology of Iceland and the North Atlantic re-
gion during the Middle and Late Quaternary: a review.
J. Quat. Sci. 15, 3–22.
Hards, V. L., P. D. Kempton, R. N. Thompson and P.
B. Greenwood 2000. The magmatic evolution of the
Snæfell volcanic centre: an example of volcanism dur-
ing incipient rifting in Iceland. J. Volcanol. Geotherm.
Res. 99, 97–121.
Heumann, A. and G. R. Davies 2002. U-Th disequilib-
ria and Rb-Sr age constraints on the magmatic evo-
lution of peralkaline rhyolites from Kenya. J. Petrol.
43, 557–577.
Hawkesworth, C., R. George, S. Turner and G. Zellmer
2004. Timescales of magmatic processes. Earth
planet. Sci. Lett. 218, 1–16.
Hubbard, A., D. Sugden, A. Dugmore, H. Norddahl and H.
Petursson 2006. A modelling insight into the Icelandic
Last Glacial Maximum ice sheet. Quat. Sci. Rev. 25,
2283–2296.
Ívarsson, G. 1992. Geology and petrochemistry of the
Torfajökull central volcano in Central South Iceland,
in association with the Icelandic hot spot and rift
zones. Unpublished PhD Thesis, University of Hawaii,
332 pp.
Jonasson, K. 1994. Rhyolite volcanism in the Krafla cen-
tral volcano, north-east Iceland. Bull. Volcanol. 56,
515–528.
Jull, M., and D. Mackenzie 1996. The effect of deglacia-
tion of mantle melting beneath Iceland. J. Geophys.
Res. 101 21815–21828.
Lacasse, C. and C-D. Garbe-Schonberg 2001. Explosive
silicic volcanism in Iceland and the Jan Mayen area
during the last 6 Ma: sources and timing of major erup-
tions. J. Volcanol. Geotherm. Res. 107, 113–147.
Larsen, G. 1984. Recent volcanic history of the Veiðivötn
fissure swarm, southern Iceland - An approach to vol-
canic risk assessment. J. Volcanol. Geotherm. Res. 22,
33–58.
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