Rock metamorphism is a geological process that changes the mineralogical and chemical composition, as well as the structure of rocks. Metamorphism is typically associated with elevated temperature and pressure, thus it affects rocks within the earth’s crust and mantle. The process is driven by changing physical and/or chemical conditions in response to large-scale geological dynamics. Consequently, it is inherent in the term, that metamorphism always is related to a precursor state where the rocks had other mineralogical and structural attributes. Metamorphism, metamorphic processes and mineral transformations in rocks at elevated temperatures and pressures are fundamentally associated with chemical reactions in rocks. Metamorphism does not include, by definition, similar processes that occur near the earth’s surface such as weathering, cementation and diagenesis. The transition to igneous processes is gradual, and metamorphism may include partial melting. The term metasomatism is used if modification of the rocks bulk composition is the dominant metamorphic process. Metamorphic rocks are rocks that have developed their mineralogical and structural characteristics by metamorphic processes <...>

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.

The papers of this volume were presented at the 109th meeting of the Princeton University Conference held in Princeton on March 10 and 11, 1972. Sponsored by the Department of Geological and Geophysical Sciences at Princeton University, in honor of Hollis D. Hedberg, the conference was attended by 140 representatives from government, industry, and the academic world. <...>