Trace element geochemistry of Raobazhai ultramafic complex, North Dabie Mountain
大别山北部饶拔寨超镁铁岩体微量元素地球化学

The major and trace element compositions of 15 samples of 5 drill cores from Raobazhai ultramafic complex are reported here. The complex is composed of upper and lower parts. The ultramafic rocks are composted of predominantly harzburgite and subordinately dunite and lherzolite. It is deduced that the ultramafic complex is a part of sub-continental lithospheric mantle with different depletion of basaltic components by partial melting of fertile mantle in different degrees from the covariance among the major element compositions of the complex. Also, the complex experienced cryptical and modal mantle metasomatism that resulted in the enrichment of incompatible elements and formation of hydrated mineral phases such as amphibole and phlogopite after mantle partial melting. Comparing LREE and LILE enrichments, it is indicated that there exist two kinds of metasomatism by two different metamorphic agencies in the complex. The LREE enrichments were probably related with silicate melt from the asthenosphere by small degree partial melting, while the LILE (for example, Rb, Ba and K etc.) enrichments were probably related with the liquid from the subduction zone by devolatilization. The effect of metasomatism in lower part of the complex was stronger than that in upper part.