Experimental petrology: Quantitative boundaries for petrogenesis

The paper is an overview of the current status on experimental petrology — its objectives and its major role in solving problems related to various earth processes. It describes how investigations related to solid-solid transitions, dehydration or decarbonation reactions, and melting studies have helped to formulate petrological models for the earth's internal structure. It also describes how measurements of physical properties of minerals, melts and vapour under extreme conditions have provided vital information of fluid dynamics of magmatic systems. The paper narrates the role of experimental petrology in calibrating geophysical processes with petrological consequences. Model P-T-X (SiO_2)-fluid systems are considered to emphasize the role of various gas species in shifting the solidus in a P-T space, in degrees of melting and composition of the melt. Synthetic models and study of whole rock systems are considered to discuss the zonation and metasomatic processes in the mantle of the earth. The paper is also concerned with mantle convection and the uprise of thermal plumes, particularly, in the oceanic environment. It discusses the petrological structures associated with the plume and shows how static petrological maps are modified by the dynamics of the plumes.