Monazite grains in igneous and high-grade metamorphic rocks often contain multiple growth zones that yield U,Th-Pb dates corresponding to multiple events in the history of a rock. The proposed lab and field experiments are designed to characterize monazite growth and recrystallization. In-situ measurements of textural features, ages, and compositions of growth zones in natural monazites collected from regions with well-characterized histories (a pluton in southern Nevada, metamorphic terranes in North Carolina and California) will help to establish the timing and conditions of monazite growth. Lab experiments conducted undersimilar conditions will quantify growth mechanisms and rates and corroborate textural interpretations of zoning in natural monazites. Because growth and recrystallization often appears to be related to fluid influx, experiments on rocks containing monazite and fluid will help to identify characteristic textural features of hydrothermal growth and recrystallization including crystal size distributions, zoning patterns, inclusion/host relations, and wetting angles. The dependence of these features on fluid composition, host grain size and coarsening rate, and temperature will also be investigated to identify conditions of growth of natural monazites. Results will refine interpretations of texture and zoning in natural monazites and the correlation of measured U,Th-Pb monazite ages with specific geochemical and tectonic events.
