Geochemistry and mineralogy of the phonolite lava lake, Erebus volcano, Antarctica: 1972 – 2004 and comparison with older lavas Peter J. Kellya,1, Philip R. Kylea, Nelia W. Dunbarb, Kenneth W.W. Simsc aDepartment of Earth and Environmental Science,New Mexico Institute of Mining and Technology, Socorro, NM 87801-4796 bNew Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, NM 87801-4796 cWoods Hole Oceanographic Institution, Woods Hole, MA, Woods Hole, 02543 1 Current address: Climate Change Research Center, University of New Hampshire, Durham, NH 03824-3525 Corresponding author: Peter Kelly Climate Change Research Center, University of New Hampshire 39 College Rd. Durham, NH 03824 E-mail:
[email protected] Fax: 603-862-2124 For submission to Special Issue on Erebus Volcano, Journal of Volcanology and Geothermal Research 14 October 2007 Word Counts: Abstract: 258 Text: 7,417 Figure Captions: 691 Table Captions: 109 References: 91 Figures: 10 Tables: 5 Keywords: Erebus volcano; phonolite; lava bombs; mineralogy; geochemistry; Antarctica Abstract Mount Erebus, Antarctica, is a large (3794 m) alkaline open-conduit stratovolcano that hosts a vigorously convecting and persistently degassing lake of anorthoclase phonolite magma. The composition of the lake was investigated by analyzing glass and mineral compositions in lava bombs erupted between 1972 and 2004. Matrix glass, titanomagnetite, olivine, clinopyroxene, and fluor-apatite compositions are invariant and show that the magmatic temperature (~1000°C) and oxygen fugacity (ΔlogFMQ = -0.9) have been stable. Large temperature variations at the lake surface (ca. 400 - 500°C) are not reflected in mineral compositions. Anorthoclase phenocrysts up to 10 cm in length feature a restricted compositional range (An10.3-22.9Ab62.8-68.1Or11.4-27.2) with complex textural and compositional zoning.