Liquid Immiscibility of Boninite in Xiangcheng, Southwestern China, and Its implication to Genetic Relationship between Boninite and Komatiitic Basalt

Boninitic rocks and associated high‐magnesian basalt and high‐iron tholeiite in the Xiangcheng area constitute the basal horizon of the arc volcanic sequence in the Triassic Yidun Island‐Arc, southwestern China. The boninite occurs as pillow, massive and ocellar lavas; the last one possesses well‐developed globular structure and alternates with the former two. The boninite is characterized by the absence of phenocrysts of olivine and low‐Ca pyroxenes and by low CaO/Al2O3ratios (<0.67) and high Cr (>1000 ppm) and Ni (>250 ppm). The normalized abundance patterns (NAP) of trace elements to primitive mantle are similar to the NAP of low‐Ca modern boninites and SHMB in the Archaean and Proterozoic.