PETROCHEMISTRY, GEOCHEMISTRY AND GENESIS OF THE META-GABBRO IN TAYUAN, NORTHERN DAXINGANLING

The genesis of the meta-gabbro occurring in Tayuan area is discussed on the basis of petrochemical and geochemical data. The petrochemistry of Tayuan meta-gabbro expresses the characteristics of alkali series of basalt. However, the content of Al₂O₃ in most rock samples is higher than 16%, indicating the characteristics of high-Al₂O₃ basalt of calc-alkaline series. In the diagram showing the tectonic environments with inactive element contents, all the samples are dropped in OIA area. The REE and trace element distribution patterns of Tayuan meta-gabbro show enrichment of LREE and incompatible elements, which is similar to the character of basalt in Azores platform as the modern E-type of enriched mantle. The deficiency of Nb and Ta, however, suggests its island-arc background. Analysis on the geology and tectonics in the area shows that Tayuan meta-gabbro was formed in marginal sea, as the deep-member of ocean island, derived from E₁-type of mantle source.