OIB-type mafic-ultramafic rocks in South Guangxi, South China: A record of interaction between Paleo-Tethys subduction and Emeishan large Igneous Province

Late Permian ultramafic-mafic igneous rocks in the Pingxiang area, Guangxi, South China include wehrlite, gabbro, diabase, and amygdaloidal basalt. Geochemical characteristics document interaction between the Emeishan Large Igneous Province (ELIP) and the mantle wedge related to subduction of the Paleo-Tethys. Gabbro and basalt show chondrite-normalized rare earth elements (REEs) and primitive mantle-normalized trace element patterns that parallel ocean island basalts (OIB) and mafic intrusions from the ELIP. Melts in equilibrium with clinopyroxenes, in both wehrlite and gabbro, have REEs and trace element compositions similar to OIB and high-Ti mafic rock of the ELIP. The clinopyroxenes also show a rift-related compositional trend and cover those from the ELIP rocks. These compositional features, along with their moderate initial 87Sr/86Sr and epsilon Nd(t) values (-0.8 to +3), are consistent with derivation from an enriched mantle plume source. This is the first time that ultramafic-mafic rocks are reported beyond the established extent of the ELIP and could represent an offshoot from the main mantle plume or indicate that the ELIP plume was considerably bigger than current proposals but has been significantly denuded by subsequent erosion. In addition, the Pingxiang rock units display slightly enriched epsilon Nd(t) values and slight negative Nb, Ta, and Zr relative to OIB rocks, indicating an enriched component in the mantle source. Formation of the ELIP spatially and temporally overlapped with subduction of the Paleo-Tethys ocean and interaction between the plume and mantle wedge accounts for the compositional diversity of the ELIP. Such interaction is probably common along the southwestern-southern margin of the Yangtze Block.