PROBLEMS OF THE PHYSICO-CHEMICAL THEORY OF PETROLOGIC PROCESSES

The processes of petrology are essentially physico-chemical and are best understood by: 1) analysis of natural formations and processes; 2) experimental investigations; 3) thermodynamic calculations and constructions. Petrological systems historically have been considered as essentially closed. However, recent work has stressed the significance of open magmatic and metamorphic systems and the mobility of certain components in the form of "transmagmatic solutions. " Of particular importance is the alkalinity (concentration of potassium and sodium oxides) of such solutions and the acid-base interactions. Similarly, the regimes of water and carbon dioxide during metamorphism have a direct bearing on mineral paragenesis and should be investigated further. The concepts of infiltrational and diffusional solutions in metasomatic processes explain features of chemical and mineralogical zonality which cannot be satisfactorily explained by the conventional "pulsational" theory of post-magmatic solutions. Also, the new hypothesis of "waves of acidic components," together with the "acid filtration effect," provides insight into specific processes such as leaching, hydrothermal differentiation, replacement, and mineralization.-- Rudy C. Epis.