In many ways, low grade metamorphic researchers are only now beginning to explore the diversity of quantitative approaches and techniques which have been so successfully applied to higher grade equivalents. The coming years should see new applications of isotope, aqueous, as well as experimental geochemistry to the study of low grade metabasites.
Elucidating the geochronology of low grade metabasites is a first-order, but tricky problem. Nevertheless, initial attempts at using K/Ar (Gallahan and Duncan, 1994; Faure and Mensing, 1993) and Rb/Sr (Evans, in press; Asmerom et al., 1991) systematics have shown promise. In particular, Evans (in press) has demonstrated that resetting of Rb/Sr igneous ages in metavolcanic rocks from northern Wales can be directly correlated with elevated integrated fluid fluxes during low grade metamorphism, as indicated by oxygen isotope systematics. Gallahan and Duncan (1994) have demonstrated the utility of using celadonite K/Ar ages for constraining the post-magmatic, temporal history of hydrothermal alteration and weathering of the oceanic crust.
Fluid flow and fluid-rock interactions within the low grade portions of hydrothermal systems are important processes which affect geothermal energy utilization, base- and precious-metal formation, as well as contaminant transport. Low grade metasomatic processes, such as those which are capable of converting mafic dikes into epidosites or ``prehnitites'' are truly impressive, yet existing models for how these largely irreversible processes proceed are still incapable of adequately simulating natural systems. Aqueous geochemical (e.g., Bettison-Varga et al., in press; Manning and Bird, in press and 1991) and experimental investigations (e.g., Rose et al, 1992) have begun to demonstrate the importance of incorporating physical (e.g. permeability and porosity) as well as chemical constraints into models of low grade metasomatic processes. Future modeling studies will also need more data bearing on the kinetic constraints (e.g., Rose, 1991) affecting these systems.
Ultimately though, field-based studies will continue as always to provide essential data for constraining these modeling and experimental studies into low grade metamorphism. Future ``field''-based studies of low grade metabasites will most certainly be conducted under water. Our understanding of low grade metamorphism in the oceanic crust is still crude in comparison to on-land equivalents. There will undoubtedly be many new and exciting discoveries in this field as drilling and submersible expeditions explore the diversity of oceanic tectonic settings.
Acknowledgments. My recent work on low grade metamorphism has been sponsored by NSF grant EAR-9203743 and ACS-PRF grant 19533-AC2. Recent advances in the study of low grade metabasites have been greatly enhanced through the activities of IGCP Project 294, masterfully guided by project co-leaders Richard Bevins and Doug Robinson. Discussions with L. Bettison-Varga, H.W. Day. and R.E. Beiersdorfer have helped to focus my thinking about the low grade metamorphism of mafic rocks. I thank J.G. Liou for his review of this manuscript, his seminal contributions to its topic, and for originally stimulating my interest in low grade metamorphism some 20 years ago.