HR: 1340h
AN: V13D-0574    [Abstracts]
TI: History of Ice Sheet Thinning in Iceland Derived From Cosmogenic ³He Exposure Ages of Subglacially Erupted Table Mountains
AU: * Licciardi, J
EM: joe.licciardi@unh.edu
AF: Department of Earth Sciences, University of New Hampshire, Durham, NH 03824 United States
AU: Kurz, M
EM: mkurz@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Curtice, J
EM: jcurtice@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AB: Table mountains in the neovolcanic zones of Iceland are widely interpreted as subglacial volcanoes that grew upward and emerged through a pre-existing ice sheet. Their characteristically flat tops can be used to define the surface elevation and thickness of the ice sheet at the time of eruption. We measured cosmogenic ³He concentrations in olivine phenocrysts from subaerially erupted basaltic lava caps of Iceland's table mountains to develop a first-order exposure age chronology of their formation. The resulting ³He exposure ages, calculated using a locally-derived calibration of the ³He production rate and comprising >40 individual ages from 13 table mountains, allow reconstruction of surface profiles of the former Iceland ice sheet through time. In the Northern Volcanic Zone, mean ages of seven table mountains range from 10.4 ± 0.4 ³He ka (Herdubreid, 1682 m elevation) to 14.4 ± 0.4 ³He ka (Snartarstadarnupur, 284 m). In the Western Volcanic Zone, preliminary ages of six table mountains range from 7.9 ± 0.3 ³He ka (Hlodufell, 1106 m) to 12.4 ± 0.5 ³He ka (Hvalfell, 806 m). The mean exposure age of Hlodufell is younger than that expected from relations with radiocarbon-dated postglacial lava flows in the vicinity, and may reflect the influence of past cover by snow or ash. Nevertheless, the new ³He chronology clearly indicates that all dated table mountains experienced their final eruptive phase during the last deglaciation. This timing of eruptive activity is consistent with hypotheses for a dynamic link between ice sheet unloading and enhanced volcanic production in Iceland. The ³He ages also suggest that initiation of ice sheet thinning coincided with or closely followed the onset of the Bølling-Allerød warm interval in the North Atlantic region.
DE: 0726 Ice sheets
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 8408 Volcano/climate interactions (1605, 3309)
DE: 8427 Subaqueous volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005