Estimation of the Primary Magma Compositions of an Igneous Rock Series Petrogenetically Associated with Fractional Crystallization with Special Reference to Element Abundance Relationships

A primary magma not only represents the starting point of a fractional crystallization process,but also is the product of an equilibrium or fractional partial melting process in a mantle. Element abundance relation ships in the primary magma obey both the law of power function for fractional crystallization and the law of fractional linear function for Nullibrium partial melting. Based on this double nature of the primary magma, the authors advanced a principle to restore the primary magma composition from that of an igneous rock series with petrogenesis of fractional crystalization and put forward an approach of estimating the element abundance of the primary magma, exemplified by the rare-earth elements in the Andes volcanic rock series.