HR: 14:10h
AN: V43E-03    [Abstracts]
TI: A new Mantle Source Tapped During Episode 55 of the Pu'u O'o Eruption From Kilauea Volcano
AU: * Marske, J P
EM: marske@hawaii.edu
AF: University of Hawaii, Department of Geology and Geophysics, Honolulu, HI 96822 United States
AU: Pietruszka, A J
EM: apietruszka@geology.sdsu.edu
AF: San Diego State University, Department of Geological Sciences, San Diego, CA 92182 United States
AU: Garcia, M O
EM: garcia@soest.hawaii.edu
AF: University of Hawaii, Department of Geology and Geophysics, Honolulu, HI 96822 United States
AU: Rhodes, J M
EM: jmrhodes@geo.umass.edu
AF: University of Massachusetts, Department of Geosciences, Amherst, MA 01003 United States
AB: Over 22 years of continuous geochemical monitoring of lavas from the current Pu'u O'o eruption allows us to probe the mantle and crustal processes beneath Kilauea Volcano in unparalleled detail. Episode 55 (1997-present) marks the longest and most voluminous Pu'u O'o eruptive interval. Here we present new Pb, Sr, and Nd isotopic ratios and major- and trace-element abundances for the most recent lavas (1999-2005). MgO variation diagrams show that most of the major-element variations are related to olivine fractionation. However, Pu'u O'o lavas display longer-term systematic decreases in their TiO2, K2O, P2O5 and CaO abundances (at a given MgO) due to changes in the parental magma composition. Incompatible element ratios (K2O/TiO2, Nb/Y, Nb/Zr) and MgO-normalized abundances (Sr, Rb, K) in episode 55 lavas delimit the lowest values observed during the Pu'u O'o eruption. Earlier Pu'u O'o lavas displayed a temporal decrease in highly over moderately incompatible trace-element ratios, near constant SiO2 contents, and a gradual increase in 87Sr/86Sr. However, episode 55 lavas (between days 5500-6500) record an increase in MgO-normalized SiO2 contents and even higher 87Sr/86Sr with near constant incompatible trace-element ratios. Neither a single mantle source composition nor a change in partial melting conditions can explain these observations. Based on 226Ra-230Th-238U disequilibria and partial melting modeling of trace elements, we conclude that Pu'u O'o lavas originate from at least two distinct mantle source components: (1) a recently depleted component that was subsequently remelted to explain the overall decreases of incompatible major- and trace-element ratios and abundances, and (2) a compositionally and isotopically distinct mantle component that was not previously melted within the Hawaiian plume to explain the temporal increase in 87Sr/86Sr and SiO2 abundances and the flattening trend of incompatible trace-element ratios. This second component lies within typical Pb, Sr and Nd isotopic space for Kilauea, but represents a new source composition for the Pu'u O'o eruption. These results can be explained by a recent (1999) change in the size or location of Pu'u O'o's melting region, which allowed this new source to be tapped.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1065 Major and trace element geochemistry
DE: 3619 Magma genesis and partial melting (1037)
DE: 3621 Mantle processes (1038)
DE: 8415 Intra-plate processes (1033, 3615)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005