中国科学院南京地质古生物研究所机构知识库

The Upper Jurassic-Lower Cretaceous Sangxiu Formation in the Rongbu area of Tibet is dominated by large-scale exposed basalts. This paper characterizes the geochemistry and magmatic activities of the Sangxiu Formation basalts in a geochemical analysis. The Sangxiu basalt has higher content of TiO2, TFeO and P2O5 (average content is 3.68%, 11.16% and 0.51%, respectively). The total amount of rare earth elements (REEs) in the Sangxiu Formation basalt is high and largely variable (ranging from 174.6 x 10(-6) to 235.3 x 10(-6)). The light-to-heavy REE ratio ranges from 6.19 to 8.36. These characteristics and the REE fractionation degree of the samples indicate an origin from the same magma. The Zr/Nb ratio of the trace elements lies between 7.96 and 13.15, and the Hf/Th ratio is 1.73-6.67, similar to those of intraplate basalts. And the basalts have the characteristics of elements similar to OIB-type basalt. The magma experienced a large degree of separation and crystallization. During the low-level partial melting of the source material, the basaltic magma of the Sangxiu Formation were isolated and crystallized by olivine, clinopyroxene and other iron-magnesium minerals but were not contaminated by the crust during their evolution. After comparison, it is found that the Sangxiu basalts have similar trace elements and Sr-Nd isotopes with the T7090 diabase and the Laguila magnesite in the Jiangya-Kangma area. It is believed that the Sangxiu basalt is the early stage of the Kerguelen mantle. The hot spot is formed by mixing with the lithospheric mantle and quickly cascade to the edge of the passive continental rift.