Jökull

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Jökull - 01.12.2006, Qupperneq 75

Jökull - 01.12.2006, Qupperneq 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. JÖKULL No. 56 73
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