Based on field observations coupled with trends in mineralogy and major element composition, Dr. M. Obata and Japanese colleagues have interpreted the layered Horoman peridotite as a "frozen" example of melt segregation in the upper mantle. In a collaborative effort with Obata and colleagues, F. Frey (MIT) and N. Shimizu (WHOI) plan to determine the trace element and isotopic (Sr, Nd, Pb) systematics of contiguous layers in this peridotite. The processes of melt formation and segregation are major, but poorly understood, mechanisms that have been in controlling the evolution of the earth's mantle and crust. The comprehensive data generated by this collaborative effort should help to define the proceses that created layering in the Horoman peridotite, and significantly improve the understanding of melt formation, migration and segregation in the upper mantle. This is a joint project with Dr. N. Shimizu of the Woods Hole Oceanographic Institution. and Dr. Fred Frey of the Massachusetts Institute of Technology.