Stromatic migmatites Term Paper Example | Topics and Well Written Essays - 2500 words

Stromatic migmatites - Term Paper Example evidence suggests that the stromatic coarse-grained rocks are formed by most of the fluid-present accompanied by equilibrium melting of the dioritic gneiss and by a crystallization dominated feldspar. Partial melting in the middle to lower crust may take place in response to dehydration of hydrous minerals such as muscovite, biotite, and amphibole or influx of externally derived hydrous fluids. (Mehnert, 1998) Geochemical evidence suggests that the melts may undergo a process leading to formation of various indigenous rocks, either  in situ  or while migrating from the site of melting  hence migmatites will form in regions of high structural forces, thickened crust and a number of field and experimental studies have indicated a significant potential for melt migration during deformation.   Despite several recent studies regarding the structure and formation of stromatic migmatites, a number of questions regarding the origin of these rocks remain unanswered. These unresolved issues include the role of fluid during partial melting i.e. whether the abundant coarse-grained rocks represent  in situ  or externally derived melts, the extent to which coarse-grained rocks compositions were modified by fractionation, and the possible relationships between melting, melt migration and the forces due to their origin. (Raymond, 2002) The purpose of this paper is to present an analysis of data from both the origin and chemical composition in an attempt to explain the geological structure of stromatic migmatites and thereby contribute to a better understanding of the causes and consequences of partial melting and other large collisional forces resulting in the formation of these structures. The two types of migmatites i.e. stromatic and patch migmatite are distinguished based on the morphology of the constituent grains and type of host rock. Stromatic migmatites are typically light grey, quartz monzodioritic to greenish gray- pinkish gray coarse-grained rocks while patch