ABSTRACT

Apatite, a common REE-enriched accessory mineral occurring in various rocks, provides important information on metallogenic source, magma evolution and source of sedimentary basin. In this study, we described an in situ method for simultaneous measurement of REE concentrations and Nd isotopic composition in apatite using a single-collector sector field inductively coupled plasma mass spectrometer and a muti-collector inductively coupled plasma mass spectrometer, connected to a single 193 nm laser-ablation system. The laser-ablated aerosol was split into two gas lines by a Y-shape joint and simultaneously transported into the two mass spectrometers. REE concentrations were measured on the SF-ICP-MS, while Nd isotopic composition was measured on the MC-ICP-MS. Two well-known apatite standards (Durango and Otter Lake) were measured to evaluate the precision and accuracy of this method. The measured Nd isotopic compositions of both apatites agree with their recommended values within analytical error. The measured REE concentrations display perfect coincidence with reported data. Using the established method, REE concentrations and Nd isotopic ratios of apatite sample from South China Sea Zhongnan and Zhenbei seamount lavas were measured. The measured data indicate that the compositional variation in apatite crystals in Zhongnan seamount is due to variable degrees of crustal contamination of the magmas during fractional crystallization, while the relatively large variability in ¹⁴³Nd/¹⁴⁴Nd ratios apatite from Zhenbei seamount most likely reflect source heterogeneity.