Improved in situ Sr isotopic analysis by a 257Â nm femtosecond laser in combination with the addition of nitrogen for geological minerals

Combining the advantages of the fs laser system with the addition of nitrogen, an improved in situ Sr isotope analytical method is then developed. The satisfactory accuracy and precision of the 87Sr/86Sr ratio from natural plagioclases, a K-feldspar with high Rb/Sr ratios (0.46) and a low-Sr clinopyroxene were obtained, demonstrating the reliability of the proposed method. Four feldspars, which have different contents of the major elements, Sr and Rb, showed homogeneous Sr isotope compositions and were recommended as potential suitable reference materials for in situ Sr isotope analysis. As an application, two plagioclases in mafic microgranular enclaves (MMEs) with small grain sizes (200-300 μm) and wide ranges of Rb/Sr ratios were analyzed and showed obvious variations of the 87Sr/86Sr ratios from core to rim, which indicated that the proposed method in this study can provide high spatial resolution geochemical information for a single mineral.