Lithospheric thickness controlled compositional variations in potassic basalts of Northeast China by melt‐rock interactions

Abstract Melt‐rock interaction is a common mantle process; however, it remains unclear how this process affects the composition of potassic basalt. Here we present a case study to highlight the link between compositional variations in the potassic basalts and melt‐rock interaction in cold lithosphere. Cenozoic potassic basalts in Northeast China are strongly enriched in incompatible elements and show EM1‐type Sr–Nd–Pb isotopes, suggesting an enriched mantle source. These rocks show good correlations between 87 Sr/ 86 Sr and K 2 O/Na 2 O and Rb/Nb. Notably, these ratios decrease with increasing lithospheric thickness, which may reflect melt‐lithosphere interaction. Phlogopite precipitated when potassic melts passed through the lithospheric mantle, and K and Rb contents of the residual melts decreased over time. The thicker the lithosphere, the greater the loss of K and Rb from the magma. Therefore, the compositions of potassic basalts were controlled by both their enriched sources and reactions with lithospheric mantle.