HR: 0800h
AN: V31C-1456    [Abstracts]
TI: Li, Be, and B Concentrations in Mauna Loa and Mauna Kea Lavas from the HSDP-2 Drill Core
AU: * Slater, V P
EM: vpslater@hotmail.com
AF: University of Tennessee, University of Tennessee, Knoxville, TN 37996-1410 United States
AU: Ryan, J
EM: jryan@nsf.gov
AF: Division of Undergraduate Education, Room 835, National Science Foundation, 4201 Wilson Boulevard, Arlington, VA 22230 United States
AU: Ryan, J
EM: jryan@nsf.gov
AF: Department of Geology, University of South Florida, 4202 East Fowler Avenue, SCA 528, Tampa, FL 33620 United States
AU: McSween, H Y
EM: mcsween@utk.edu
AF: University of Tennessee, University of Tennessee, Knoxville, TN 37996-1410 United States
AB: Continuous core samples collected during Phase 2 of the Hawaii Scientific Drilling Project (HSDP-2) provide the most complete time sequence stratigraphy for a hotspot volcano. 43 samples, representing 245 m of Mauna Loa (ML) tholeiitic lavas and 2853 m of Mauna Kea post shield (MKPS) and main shield (MKMS) alkaline and tholeiitic lavas, were analyzed for whole-rock Li, Be, and B abundances to determine how these elements vary as the volcano samples the Hawaiian plume. Anomalous Sr/MgO variations indicate that MKPS lavas have experienced alteration. Highly scattered B abundances (1.1-9.4 ppm), B/K ratios (0.0002-0.008), and B/Be ratios (1-25) suggest substantial remobilization of this H$_{2}$O-soluble element. Regular correlations between Be and MgO, Zr and Nd indicate that Be behaves incompatibly in HSDP lavas. Be ranges from 0.28-0.54 ppm in ML, 0.52-0.97 ppm in MKPS, and 0.23-0.71 ppm in MKMS lavas. Be/Nd = 0.03$\pm$0.005, slightly lower than MORBs or chondrites. Li ranges from 2.5-6.1 ppm and does not vary among lava types. Li/V ($\sim$0.02) and Li/Y ($\sim$0.18) ratios are similar to MORBs, but Li/Yb (2.3) ratios are higher than MORBs. Despite evidence for weathering in MKPS lavas, Li correlates well with Be, Nb, Zr, Y, Yb, and V, suggesting Li was not mobilized with alteration. However, such correlations do not occur in ML or MKMS lavas, indicating Li modification. The lack of change in Be/Nd, Li/V and Li/Yb shows abundances of these elements are governed largely by extent of melting and/or crystallization. Mantle compositions for these species do not seem to vary on the timescale of shield development. B and (to a lesser extent) Li are useful indicators for alteration and/or hydrothermal activity within shield edifices. Lentz et al. (2001) used variations in B and Li content in pyroxenes of some Martian meteorites to suggest these elements were lost (along with H$_{2}$O and CO$_{2}$) as the magma degassed during ascent. Since mantle plumes were the primary means for Mars volcanism, the Hawaiian plume may serve as a terrestrial analog for understanding geochemical variations in Martian meteorites.
DE: 1025 Composition of the mantle
DE: 1065 Trace elements (3670)
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting