GEOCHEMICAL INVESTIGATION OF ANATECTIC MELTS IN LOW-PRESSURE MIGMATITES

The study of melt inclusions is vital to understanding igneous processes. Inclusions trap and preserve melts prior to subsequent processes including crystallization, diffusion, and any potential disequilibria the crystals may be subjected to, as well as chemical weathering or alteration at the surface. In many cases, they also retain their concentration of volatile elements. These advantages make melt inclusions highly valuable in studying the evolution of magmatic systems. Although they have been utilized extensively in volcanic systems and in some felsic plutonic systems, recent studies have suggested they may be found in other plutonic rocks and potentially in metamorphic rocks undergoing partial melting. Questions remain regarding the latter due to the difficulty in distinguishing between silicate melts and Si-rich hydrothermal fluids at high pressures. Additionally, these melt inclusions are usually completely crystallized and are difficult to identify. The focus of this study aims at finding and determining the geochemistry of melt inclusions in low-pressure migmatites. These trapped melts would thus represent the exact conditions present at the time of anatexis. Migmatites are unusual rocks as they are partially melted and represent a transition between igneous and metamorphic. Samples were collected over the course of a week from previously described field locations in New Hampshire and Maine. This project will explore the geochemistry and petrogenesis during the initial stages of anatexis. Homogenization experiments of potential melt inclusions will determine whether they truly represent melts that subsequently crystallized or trapped solids. Samples were crushed and separated to identify potential melt inclusion-bearing crystals of peritectic minerals such as garnet, cordierite, and spinel that are preserved over the course of melting and subsequent crystallization. Finally, the geochemistry of both the inclusions and their host crystals will be determined via electron microprobe that will allow for in-situ analysis of major and minor elements.