HR: 0800h
AN: V21D-0655    [Abstracts]
TI: Crustal Control on Crystallization Depths? Preliminary Evidence from Mt. Cleveland, Chuginadak Island, Eastern Aleutian arc
AU: * Nicolaysen, K P
EM: knic@ksu.edu
AF: Department of Geology, Kansas State University, Manhattan, KS 66506
AU: Bridges, D
EM: dbridges@ksu.edu
AF: Department of Geology, Kansas State University, Manhattan, KS 66506
AU: Swapp, S
EM: swapp@uwyo.edu
AF: Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071
AB: Mt. Cleveland is one of the most active volcanoes of the eastern Aleutian arc with eruptions in 2005 and 2001 and a total of 23 known eruptions in approximately the last hundred years. Several features, perhaps indicating a complex crustal geometry make Mt. Cleveland unusual. First, the Islands of Four Mountains (Herbert, Carlisle, Cleveland, Tana, Kagamil) define an area of unusually closely-spaced Quaternary stratovolcanoes relative to the central and western Aleutians. Also, the Islands of Four Moutains are closer to the trench compared to the rest of the arc. Finally, the earthquake record shows a linear cluster of earthquakes leading from Cleveland toward the trench (map view); as yet, no interpretation exists to explain how the defined linear feature may relate to a crustal structure or the downgoing slab. The crust beneath the volcano is approximately 30 km thick and is transitioning from oceanic to continental affinity. We use clinopyroxene thermobarometry to investigate the depths at which Mt. Cleveland magmas tend to stall prior to eruption to examine whether basement structure may influence the ascent of the magmas. The peak consists largely of lavas and interbedded debris flows although several cinder cones and andesitic domes have formed within five kilometers of the summit. The lavas are primarily calc-alkaline andesites and most contain two pyroxenes, plagioclase and occasionally olivine or titanomagnetite. Two of the cinder cones, in contrast, are olivine-plagioclase-clinopyroxene basaltic andesites. Preliminary data show that a Holocene flow (1994?) from Mt. Cleveland crystallized clinopyroxene at approximately 1035°C and 13+/-2 kb pressure, which corresponds nearly with the base of the crust. In contrast, the 2001 tephra essentially crystallized at 1 atm, consistent with rapid ascent through the crust. The basaltic andesite of the youngest cinder cone crystallized clinopyroxene at approximately 1300°C and 3 kb pressure, indicating some residence time in the crust.
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3651 Thermobarometry
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8185 Volcanic arcs
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005