Abstract:Source components and genesis of continental intraplate basalts are pivotal to understanding the chemical heterogeneities and geodynamic processes of the Earth's mantle. Since different mantle end members have different H2O values and H2O/incompatible element (such as H2O/Ce) ratios, the H2O content of primary basaltic magma might provide constraints on source components of continental intraplate basalts. Quenched glasses and melt inclusions in phenocrysts are commonly used to obtain the water content of primary magma of oceanic basalts, but they cannot provide useful information concerning the water content of primary magma for continental basalts. On the one hand, continental basaltic glasses usually experienced highly degassing when they were erupted at the surface due to the lack of water pressure to oceanic basalts, thus causing underestimation of the true water content. On the other hand, melt inclusions in phenocrysts in continental basalts are rare and very tiny (<20 μm), which hinders accurate analysis of large quantities of samples. This paper introduces a newly developed method for estimating the water content of primary magma of continental basalts. The H2O values of clinopyroxene phenocrysts in basalts are determined by FTIR, and those of equilibrated melts are calculated through partition coefficients of H2O between clinopyroxene and basaltic melt. When the effects from degassing, assimilation and fractional crystallization during magma ascent are evaluated, the H2O content of primary magma of continental basalts can be estimated. The feasibility of the method, the evaluation of the uncertainty and the detailed operation procedure have been described. With this method, the H2O content of the Cenozoic alkali basalts from Shuangliao of Northeast China and Taihang Mountain of NCC have been estimated. Combined with other geochemical index, these new data provide additional information on the source components of basalts.