Geochemistry of extreme high Ti/Y mafic rocks from western Guangxi: Implications for the primitive magma of high Ti basalt of Emeishan mantle plume?

Bama area in western Guangxi is located on the southwestern margin of the South China Block and the northern side of North Vietnam Block. Late Permian mafic rocks are well cropped out around Bama County. Deciphering the petrogenesis of Bama mafic rocks is crucial to the understanding of the tectonic-magmatic evolution of western Guangxi. This paper presents geochemical data （major and trace elements data） of Bama mafic rocks and discusses the petrogenesis and mantle sources of Bama mafic rocks. Studies indicate that the Bama mafic rocks mainly belong to alkaline basalt. These rocks are relatively enriched in LREE and Nb, Ti, and have similar trace element characteristics to the high Ti basalts from the Emeishan mantle plume, suggesting that they shared a common mantle source. However, the Bama mafic rocks show relatively higher Ti/Y ratios than the Emeishan high Ti basalts. The incompatible trace elements ratios covariance diagram that can trace the mantle source reveals that the Bama mafic rocks have an extremely high Nb/Y evolution trend. According to Dy/Dy? versus Dy/Yb and Ti/Y covariance diagrams, the authors hold that the Bama high Ti/Y mafic rocks experienced a lower degree mantle partial melting than the Emeishan high Ti basalts, although they likely shared the same mantle plume source. Thus, the Bama mafic rocks are magmatic products in the outer zone of the Emeishan Large Igneous Province and probably represent the primitive magmas of Emeishan high Ti basalts.