HR: 1340h
AN: T53B-1312    [Abstracts]
TI: Trace Element Study of MORB Glasses from 14¡ã-16¡ãN along Mid-Atlantic Ridge by LA-ICP- MS
AU: * Barzoi, C A
EM: cabarzoi@mail.uh.edu
AF: Geosciences Department, University of Houston, 4800 Calhoun Rd. Science and Research Buliding 1, R312, Houston, TX 77204, United States
AU: Casey, J F
EM: jfcasey@uh.edu
AF: Geosciences Department, University of Houston, 4800 Calhoun Rd. Science and Research Buliding 1, R312, Houston, TX 77204, United States
AU: Gao, Y
EM: yongjungao@uh.edu
AF: Geosciences Department, University of Houston, 4800 Calhoun Rd. Science and Research Buliding 1, R312, Houston, TX 77204, United States
AU: Lapen, T
EM: tjlapen@uh.edu
AF: Geosciences Department, University of Houston, 4800 Calhoun Rd. Science and Research Buliding 1, R312, Houston, TX 77204, United States
AB: A comparison of 20 MORB glasses from 14\textdegree{}-16\textdegree{} N along the Mid-Atlantic Ridge using both solution-based and in situ laser ablation-based ICP-MS trace element analyses on the same samples was conducted. Li, Be, Sc, Ti, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Ba, La, Ce, Pr, Nd, Sm, Eu, Tb, Gd, Dy, Ho, Er, Tm, Yb,Lu, Hf, Ta, Pb, Th, and U were analyzed using the Varian 810 quadrupole ICP-MS. The instrument features a 90 degree ion mirror and low noise double-off-axis quadrupole that allows high sensitivity and low backgrounds. Precision in term of relative standard deviation (RSD) of the measurements for both methods based on repeated analyses of USGS BIR-1G and BHVO-2G glass standards and Max Planck KL-2G glass standard is within 5 % for all trace elements with the exception of Pb, which averaged 12 %. Measured trace element abundances are within 2% of recommended standard values using both solution and laser ablation methods. Comparison between the analyte concentrations obtained by solution-based ICP-MS and in situ microanalysis by laser ablation reveals little systematic differences in abundances(\begin{math}<\end{math}5% for all elements). The two-method correlation and strong repeatability of the results indicate that rapid in situ trace element analysis by laser ablation ICP-MS is likely to become a preferred method of trace element analysis for MORB glasses. Our geochemical results and previous studies of MORB glasses in the region of the MAR between 14\textdegree{}-16\textdegree{}N show that basalts are characterized isotopic and incompatible element enrichment.The nature of the enrichment has been the topic of significant discussion and speculation because a specific mantle plume is not well defined in the region. Likewise the magma supply is probably small in the region as the magmatic crust is interpreted to be very thin in most of the area studied. Integrated studies of major element, trace element, and isotopic variations among basalts, gabbroic rocks and igneous and residual ultramafic rocks in the region indicate that 1) the enriched basalts have positive Ta-Nb anomalies, enriched relative to U, Th, and La 2) basalts have relatively high SiO₂ abundances compared to the global average, 3) basalts show a HIMU isotopic signature, and 4) bulk major element abundances and mineral chemistry in mantle rocks indicate that they are among the most depleted,although variably refertilized, residual mantle assemblages sampled to date along MORs.We suggest that much of the regional variation in major and trace element data, as well as isotopic data and the unusual regional geology (multiple core complexes) can be explained by melting of a sub-axial mantle that contains two end members, one highly depleted and the other enriched. These components appear to involve ancient recycled ocean crust and lithospheric mantle.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 3035 Midocean ridge processes
DE: 8150 Plate boundary: general (3040)
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting