Determination of Sm-Nd Isotopic Compositions in Fifteen Geological Materials Using Laser Ablation MC-ICP-MS and Application to Monazite Geochronology of Metasedimentary Rock in the North China Craton

In this study, we report both Nd-143/Nd-144 and Sm-147/Nd-144 values in twelve minerals (apatite, titanite, monazite and eudialyte) based on analyses over 4years using LA-MC-ICP-MS. The positive correlation between the measured (Sm) and (Nd) (r(2)=0.9981) over this time in our laboratory demonstrates the excellent long-term stability of the method. Compared with the normal method, Sm and Nd signal intensities were improved by a factor of 2.9 with the use of X skimmer and Jet sample cones in combination with the addition of nitrogen at 3-6mlmin(-1) to the central gas flow. The enhancement of signal intensity benefits the accurate insitu determination of the Sm-Nd isotopes of samples poor in these elements. Nd-143/Nd-144 values were also determined in two manganese nodules and GSMC Co-rich crust with low mass fractions of Nd (94-293gg(-1)). Generally, most of the obtained Sm-Nd isotopic compositions in these geological materials are consistent with published values. External reproducibility' (2s) of Nd-143/Nd-144 and Sm-147/Nd-144 was typically better than 0.06 parts per thousand and 2.5 parts per thousand, respectively, demonstrating that the Durango, Otter Lake, NW-1 and MAD apatites, the Khan, and OLT-1 titanites, MGMH#117531 monazite and LV01 eudialyte are promising candidate reference materials for insitu Sm-Nd isotopic determinations. The Trebilcock, Mae Klang and 44069 monazites are only suitable for insitu Nd isotopic determinations because of their heterogeneous Sm/Nd compositions. The heterogeneous Sm-Nd composition of titanite BLR-1 demonstrates that it is not a suitable reference material for insitu Sm-Nd isotopic determinations. Deep-sea samples (NOD-A-1 and NOD-P-1 manganese nodule, GSMC Co-rich crust) with low mass fractions of Nd also show homogenous Nd isotopic compositions. Sm-Nd isotopic ratios of a monazite (MQG-22) from the North China Craton were measured as a case study and gave a Sm-147-Nd-143 isochron age of 1792 +/- 35Ma (MSWD=3.2) consistent with the published metamorphic age of the host metasedimentary rocks. The results for both candidate reference materials and geological samples demonstrate that the insitu LA-MC-ICP-MS analytical protocol described is feasible and robust for research in geological evolution.