HR: 1330h
AN: V12D-0614    [PDF]
TI: Closed System Behavior of Trace Elements During Basalt Crystallization in the Makaopuhi Lava Lake, Hawaii.
AU: * Hagerty, J J
EM: jh2713@unm.edu
AF: Institute of Meteoritics, 1-University of New Mexico MSCO3 2050, Albuquerque, NM 87131 United States
AU: Shearer, C K
EM: cshearer@unm.edu
AF: Institute of Meteoritics, 1-University of New Mexico MSCO3 2050, Albuquerque, NM 87131 United States
AB: The Makaopuhi Lava Lake formed during an eruption of the Kilauea volcano in March 1965. During a U.S.G.S. study of the lava lake (Wright and Okamura, 1977), direct measurements were made of the thermal history, oxygen fugacity, volatile content, petrography-chemistry, viscosity, and density. These observations provide a unique opportunity to place trace element behavior into the context of a well-defined, natural magmatic system. Samples used in this study were collected at temperatures between 1160 and 990§C and at an approximate fO2 equal to the NiNiO buffer. All samples represent coexisting crystals and glass. The crystallization sequence within the lake was: olivine, augite, plagioclase, ilmenite, pigeonite, magnetite, apatite. During crystallization the olivine composition ranges from Fo85 to Fo50 and the MgO of the melt ranges from 3 to 9 wt.%. Trace element measurement (K, V, Cr, Mn, Co, Ni, Y, Sm, and Th) on individual phases were made using secondary ion mass spectrometry. Absolute concentrations of each element for each phase were calculated using empirical relationships of Trace Element/30Si+ ratios, which were normalized to known SiO2 content. Our initial results show that as the temperature decreases, the melt composition exhibits a predictable decrease in Ni, Co, and Cr, a minor increase in Mn and V, and substantial increases in K, Y, Sm, and Th. Nickel and Cr decrease from olivine core to rim, whereas Mn, Co, and V exhibit limited variation from core to rim. The behavior of trace elements between olivine and melt changes systematically with decreasing temperature. The distribution coefficients (D ol/melt) for highly incompatible elements such as K, Y, Sm, Th decrease with decreasing temperature. The D (ol/melt) for Ni remains the same over much of the temperature range (15), but increases dramatically at very low temperatures. The D (ol/melt) for Cr, V, Mn, and Co systematically increase with decreasing temperature.
DE: 1065 Trace elements (3670)
DE: 3640 Igneous petrology
DE: 3670 Minor and trace element composition
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting