Origin of Late Permian Emeishan basaltic rocks from the Panxi region (SW China): Implications for the Ti-classification and spatial-compositional distribution of the Emeishan flood basalts

Basalts and a mafic dyke collected from the city of Panzhihua show characteristics of high-Ti and low-Ti Emeishan basalts respectively. The dyke yielded a SHRIMP zircon U-Pb mean age of 261±5Ma making it contemporaneous with the eruption of Emeishan basalts. The basalts have I_Sr ranging from 0.7059 to 0.7062 with εNd_(T) ranging from -1.1 to +0.7 whereas the dyke has I_Sr ranging from 0.7056 to 0.7064 with εNd_(T) ranging from +0.3 to +0.5. Trace element modeling shows that the two rock types can be generated by different degrees of partial melting from the same garnet-bearing source. Assimilation of crustal material is required in order to produce the depletion of some trace elements (e.g. Nb and Ta) of the dyke however crustal assimilation is not required to produce the basalts. Trace element modeling and isotopic data of the Emeishan basalts suggest that, in general, the high- and low-Ti basaltic rocks are likely derived from the same source and represent different degrees of partial melting with or without crustal assimilation. The location and geological relationships of the 'high-Ti' basalts indicate they erupted relatively early and within the central part of the ELIP, casting doubt on the previous spatial-compositional distribution of the Emeishan basalts.