Petrogenesis of Cenozoic Basaltic Rocks from the Leiqiong Area, South China: Evidence from Geochemical Constraints

Abstract

In the present study, based on major, trace, and rare earth elements and isotopic ratios of the basaltic rocks, we suggest that the basalts from Hainan Island and Leizhou Peninsula are derived from different magma series, which may be produced by different degrees of partial melting of the OIB-like mantle source. Geochemical characteristics of trace elements show that a recycled oceanic crust component is involved in the source mantle, which may have been metasomatized by fluids (e.g., H2O and CO2) before the partial melting process. We propose that the degree of partial melting that generates the basalts from Leizhou Peninsula (3-12%) is larger than the degree generating the basalts from Hainan Island (1.7-10%). Sr-Nd isotopic data imply that Leiqiong basalts represent mixtures of melts derived from depleted Indian Ocean mid-ocean ridge basalts (MORB)-like or depleted MORB mantle (DMM) and enriched mantle type 2 (EM2). Our geochemical evidence and previous study results support that the Leiqiong basaltic magma may be generated by the Hainan mantle plume. On the basis of the chemical compositions of Leiqiong basalts, we conclude that the EM2-type lithospheric mantle may be heated by an upwelling mantle plume produced by the primary basaltic magma; subsequently, fractional crystallization of olivine, clinopyroxene, Fe-Ti oxides (ilmenite or titanomagnetite), and plagioclase probably occurred during magmatic evolution.