HR: 0800h
AN: V41A-0392    [Abstracts]
TI: Iceland Deep Drilling Project (IDDP): (IV) Fluid Inclusion Microthermometry of the Geitafell Hydrothermal System – a Possible Analog of the Active Krafla System
AU: * Troyer, R
EM: rtroyer@uoregon.edu
AF: Dept. of Geological Sciences, Univ. of Oregon, Eugene, OR 97403, United States
AU: Reed, M H
EM: mhreed@uoregon.edu
AF: Dept. of Geological Sciences, Univ. of Oregon, Eugene, OR 97403, United States
AU: Elders, W A
EM: wilfred.elders@ucr.edu
AF: Dept. of Earth Sciences, Univ. of California, Riverside, CA 92521, United States
AU: Fridleifsson, G O
EM: gof@isor.is
AF: Hitaveita Sudurnesja Ltd, Brekkustig 36, Reykjanesbaer, IS 260, Iceland
AB: The Miocene Geitafell volcanic complex in southeast Iceland hosts an extinct high temperature hydrothermal system that provides an excellent opportunity for study of the interior of an analog to the Krafla and Hengill active systems, which will be penetrated by IDDP drilling. The Geitafell volcano formed on the central Icelandic rift zone at approximately 5-6 Ma. Glacial erosion has exposed the deep interior of the volcano, revealing a complex of tholeitic lavas, hyaloclastites and rhyolites, cut by 12 intrusive phases and a sequence of seven related vein sets with distinct vein fillings and alteration haloes. Mineralogical studies by Fridleifsson (1983) show that when Geitafell was active, it hosted a supercritical hydrothermal system with fluids exceeding 400°°C at pressures up to 300 bar. We have begun fluid inclusion microthermometry studies of this system with the goal to define the specific relationship of the vein sequence to vein temperatures and alteration haloes, and thereby improve the understanding of supercritical hydrothermal systems . We have sampled veins in a basaltic lava from Fridleifsson's vein sets 2 and 3, and a quartz-filled amygdale tied to vein set 2. Vein set 2 is bordered by a narrow (5-10mm) dark alteration halo of chlorite and albite; set 3 veins have cm-scale epidote-rich envelopes. Fluid inclusions were not visible in the quartz and epidote of vein set 3, but quartz in vein set 2 contains abundant fluid inclusions 5 to 15 micrometers in size with vapor bubbles ranging from 10 to 60 vol%. In the amygdale, fluid inclusions are 5 to 30 micronmeters in size with vapor bubbles ranging from 25 to 60 vol%. The average freezing point depression for vein set 2 and amygdale inclusions is 0.1°°C, indicating a salinity of 0.2 wt% NaCl equivalent--largely fresh water. Fluid inclusions homogenize to liquid or to vapor at temperatures ranging from approximately 300 to 394°°C. Most liquid-dominated inclusions homogenize between 300 and 380°°C. The coexisting vapor rich and liquid rich inclusions and the homogenization behavior indicate a boiling hydrothermal system at a temperature of at least 380°°C.
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1043 Fluid and melt inclusion geochemistry
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting