| This thesis investigated the analytical method of Sr compositions in silicate rocks and clinopyroxene by LA-MC-ICP-MS in the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan), and evaluated the analytical method of Li isotope compositions in silicate rocks by LA-MC-ICP-MS. In addition, the Sr isotope compositions of clinopyroxenes in peridotite xenoliths collected from the Hannuoba region were determined using LA-MC-ICP-MS in order to understand the evolution of lithospheric mantle beneath the Hannuoba region. The major conclusions are listed as following:1. Er and Yb interferences on Sr isotopic determination should be corrected. Sr isotopic compositions of Sr standard solution (NBS987) doping interference elements (Ga, Fe, Zn, Er, Yb) were determined using a desolvating nebulizer (Aridus II) coupled with MC-ICP-MS to evaluate the effects of polyatomic and double charged ions on Sr isotopic analysis in details. The results show that the oxides of Ga, Zn and Fe have negligible effects on Sr isotope analysis, and the polyatomic ions of Ca could affect 84Sr/86Sr measurement but not 87Sr/86Sr measurement. But, double charged ions of Er and Yb could affect Sr isotopic determination, thus should be corrected during the 87Sr/86Sr determination. Accurate 87Sr/86Sr ratios could be obtained applying the correcting method established in this work.2. No sensitivity enhancement of Sr by adding N2 to the central channel of ICP. Although using GE leds to a 2-fold sensitivity enhancement, it significantly increased the yield of polyatomic ion interferences of Ca-related ions and TiAr+on Sr isotopes.3. Sr isotopic compositions in clinopyroxene and silicate glasses could be accurately determined by LA-MC-ICP-MS. Rb interference was corrected using virtural Rb abundance ratio, Kr interference was corrected by OPZ (On Peak Zero). Applying the method established in this work,87Sr/86Sr ratios (Rb/Sr< 0.14) of silicate glasses and natural clinopyroxenes can be accurately measured with internal precisions (2SE) of 0.0009-0.00007, depending on the Sr contents (482-30 μg g-1), and with an external precision of 0.0004 (2SD, n= 33) for a sample with 100 μg g-1 Sr.4. Laser induced isotopic fractionation, mass-loaded effect and matrix effect may have effects on Li isotopic determination by LA-MC-ICP-MS. Li isotope compositions of the international standard materials (USGS and MPI-DING) were determined by LA-MC-ICP-MS calibrated against reference material BCR-2G. 7Li/6Li ratios of ultrabasic glass varied with ablation time, suggesting the existence of laser induced isotopic fractionation. In addition, the determined δ7Li of ATHO-G with the highest Li content is lower than the reference value, indicating the exsit of mass-loaded effect. Li isotope compositions of ultrabasic glass of GOR128-G and GOR132-G were not always accurately determined, suggesting the existence of matrix effect.5. The application of Sr isotope analysis by LA-MC-ICP-MS in earth science. Lithospheric mantle beneath Hannuoba has experienced a complex mantle metasomatism. However, the nature and origin of melt/fluid reacting with mantle peridotite have not been well constrained. Sr isotopic compositions of the clinopyroxenes in peridotite xenoliths collected from the Hannuoba basalt were analyzed by LA-MC-ICP-MS. These clinopyroxenes have variable 87Sr/86Sr ratios (0.7023-0.7034). Combined with the trace elements in clinopyroxene, it was suggested that the metasomatism fluid might be derived from the subducting Paleo-Asian Oceanic crust under the North China Craton. |
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