Petrogenetic interpretation of granitoid rock series using multicationic parameters / Петрогенетическая интерпретация толщи гранитоидных пород по мультикатионным параметрам

Granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la Roche and his coworkers. This shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas. Possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors. These suggest that most granitoid series result from a two-stage process. First, fractional crystallisation of clinopyroxene, olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition. This magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series.