The Pb isotopic geochemistry of carbonatites from the Maoniuping REE deposit, China
牦牛坪稀土矿床碳酸岩Pb同位素地球化学

The carbonatite-syenite complexes in the Maoniuping REE deposit, Sichuan province, which are spatially and temporally associated with rare earth mineralization, were emplaced at the time of Himalayan. They show similar ~(206)Pb/~(204)Pb and ~(208)Pb/~(204)Pb ratios, but the carbonatites show large spread in ~(207)Pb/~(204)Pb ratios and lower than those for syenites. This reflects the characteristics of their mantle source, rather than crustal contamination. In Sr-Nd-Pb diagrams, the carbonatites and syenites are characterized by lower Pb and higher Sr isotopic ratios. The Pb isotopes for carbonatites are plotted to the range of the MORB, while the Sr and Nd isotopes are different to the MORB, relatively close to the EM1 of the OIB. The Yangtze plate was penetrated as a wedge into the crust at Longmenshan during the Himalayan period. The extruded middle and lower crust onwards subducted and extended into the enriched mantle in the top of the Panxi rift. This was followed by variable degrees and discrete partal melting of the metasomatized enriched mantle to produce alkali magma. The whole evolutionary process resulted in inhomogeneity of the mantle source.