Search

Copyright of Geostandards & Geoanalytical Research is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geostandards & Geoanalytical Research is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: In situ U–Pb dating and trace element analysis of zircons, combined with a textural relationship investigation in thin section, is a powerful tool to constrain the ultra high-pressure stage of high-grade metamorphism. Two types of zircon grains have been identified in thin sections of a retrograde eclogite from the main hole of the Chinese Continental Scientific Drill project in the Sulu UHP terrane. Type 1 zircon grains occur as inclusions in fresh garnet and omphacite, and Type 2 zircon grains were found in symplectite around omphacite. The fresh rims of Type 1 zircons and mantles of a few Type 2 zircons exhibit remarkably lower REE, Y, Nb and Ta contents than the inherited zircon cores, suggesting coeval growth with garnet, rutile and apatite during UHP metamorphism. These may have formed in the UHP metamorphism and survived retrograde metamorphism. The weighted average 206Pb/238U age of these zircon domains (230±4Ma, 2σ) agrees well with the published age of coesite-bearing zircon separates (230±1Ma, 2σ), suggesting that the peak UHP metamorphism in the Sulu terrane may have occurred at ~230Ma. Zircon domains surrounded or cut across by symplectite could have been altered by retrograde metamorphism. Together, they provide a younger weighted average 206Pb/238U age of 209±4Ma (2σ). These retrograde zircon domains have similar REE compositions to the ~230Ma UHP zircon domains. These observations imply that the ~209Ma zircon domains could have formed by fluid activity-associated alterations in the amphibolite-facies metamorphism, which could have resulted in the complete loss of Pb but not REEs in these domains. [Copyright &y& Elsevier]

Despite the large number of successful applications of LA-ICP-MS, elemental fractionation remains the main limitation for many of its applications in the Earth sciences. This limitation is particularly notable for high spatial resolution analysis. Elemental fractionation and mass-load effect in silicate glasses NIST SRM 610 and GSE-1G were investigated by using 193 nm ArF excimer nanosecond (ns) laser and 257 nm femtosecond (fs) laser ablation systems coupled to inductively coupled plasma mass spectrometry. Contrary to those observed in ns-LA-ICP-MS, the most elemental fractionation at the small spot sizes of 16–24 μm are lower than that at the large spot sizes of 44–60 μm in fs-LA-ICP-MS. The significantly different fractionation behaviors of Li, Na, Si, K, V, Cr, Mn, Fe, Co, Ni, Cu, Rb, Cs and U between silicate glass materials NIST SRM 610 and GSE-1G observed in 193 nm excimer LA-ICP-MS are eliminated by using 257 nm fs-LA-ICP-MS at high spatial resolution. In addition, the mass load effect and matrix dependent mass load effect are also found to be reduced by using fs-LA-ICP-MS in comparison with ns-LA-ICP-MS. Except for Sb, Pb and Bi, the elemental fractionation is independent on the laser fluence chosen, which is irrespective of ns- or fs-LA-ICP-MS. In this study, a spot size of 24 μm was used to test the capabilities of LA-ICP-MS analysis at high spatial resolution. The agreement between our data and the reference values is better than 10% for most of the elements in MPI-DING, USGS, and NIST glasses by using fs-LA-ICP-MS. For ns laser ablation analysis, the accuracy is highly dependent on the calibration strategies used (conventional external calibration method or 100% oxide normalization method) and the selected external reference materials (NIST SRM 610 or GSE-1G). The much less laser-induced elemental fractionation and matrix effect in fs-LA-ICP-MS in comparison with 193 nm excimer LA-ICP-MS make it more suitable for the analysis of silicate materials at high spatial resolution. [ABSTRACT FROM AUTHOR]

Abstract: Here we describe an internal standard-independent calibration strategy for LA–ICP-MS analysis of fifty-four major and trace elements in carbonate. Based on the normalization strategy of bulk components as 100%, the MRM-NoIS (calibrated against multiple silicate reference materials without using internal standard) was used to correct the matrix-dependent absolute amount of materials ablated during each run. Applying MRM-NoIS and using the MPI-DING reference glasses as reference materials for external calibration, analyses of carbonate standard MACS-3 generally agree with recommended values within 10% for most trace elements (better than 5% for REEs and major elements). Analyses of natural igneous calcite grains agree with the results of solution-ICP-MS values within 10% for Mg, Sc, Mn, Sr and REEs. The results indicate that, applying MRM-NoIS and using MPI-DING reference glasses as multiple reference materials for calibration, carbonate can be accurately analyzed in situ by LA–ICP-MS without applying internal standardization and matrix matching external standards. Our results also indicate that the working value of Nb in carbonate pellet MACS-3 could be 53.4μg/g rather than 35.2μg/g given in the test of G-Probe 4. [Copyright &y& Elsevier]