Origin Of Permian Extremely High Ti/Y Mafic Lavas And Dykes From Western Guangxi,SW China:Implications For The Emeishan Mantle Plume Magmatism

Late Permian mafic flows and dikes are prominent features in and around the Western Guangxi region in southern China.Where is located in southwestern margin of the South China Block and northern side of North Vietnam Block,a layered or small layered rock mass production.In this paper,we presented the geochemical data?major and trace elements data?of Bama-Yufeng-Longchuan-Shijia mafic rocks and discussed the petrogeness and mantle sources of Guixi mafic rocks:1)In this paper,we study the Guixi mafic rocks originated in the late Permian.The types of the western Guangxi mafic rocks are diabase and basalt,belong to the alkali basalt series.2)The mafic rocks,which are distributed in western Guangxi,have high Ti O2 content,high Ti / Y ratio and high REE,and they are rich in the light rare earth,also they have a REE distribution patterns type that lean to the right,showing that they are very similar to the oceanic island basalts?OIB?on geochemical characteristics,suggesting that maybe they are formed in the plate environment.3)Based on petrographic,geochemical and Sr-Nd isotopic data,the western Guangxi mafic rocks are geochemically akin to the Emeishan large igneous province?ELIP?high-Ti basalts,except that they possess extremely elevated Ti/Y ratios?750–2000?.4)The Dy/Yb and Ti/Y vs.Dy/Dy* covariations of the mafic rocks indicate a garnet-controlled magmatic differentiation of a mafic melt at relatively great depth.The limited ?Nd?t?range from +0.41 to +1.81 also suggests minimal crustal contamination of such a melt.5)Geochemical modeling using TiO₂/Yb vs.Nb/Yb and Zr/Y vs.Nb/Y projections indicate that the parental melts of the western Guangxi mafic rocks formed at a low degree?<5%?of partial melting at or over 3.5 GPa,consistent with a deep mantle plume source under a thick continental lithosphere.6)The Guangxi extremely high Ti/Y mafic rocks most likely represent a part of outer zone of the ELIP plume magmatism.Results of this study reinforce the previously proposed temporal and spatial distribution of the ELIP.7)We suggest that the Guangxi extremely high Ti/Y mafic rocks experienced a lower degree mantle partial melting than the Emeishan high Ti basalts,although they likely shared a same mantle plume source.This paper presents an idea that the western Guangxi mafic rocks belong to the alkali basalt series and formed in the plate environment,may be the product of the Emeishan mantle plume activity,are not only related to the basalts of Emeishan large igneous province,but also part of it.