CO2, melts and granulite metamorphism

Abstract

The discovery that granulites contain CO2-rich fluid inclusions while amphibolites in the same terrane contain H2O-rich or mixed CO2–H2O inclusions1 has led to a debate over the processes that produce granulite metamorphism. One theory2–4 maintains that granulites form as the result of a massive influx of CO2 from lower crustal or mantle sources. Such an influx could be responsible for the marked depletion many granulite terranes show in large-ion lithophile elements2,5. Others, however, maintain that granulite-facies metamorphism is a necessary complement of crustal melt ing6–9. Recently, Lamb and Valley10,11 have argued that granulite metamorphism may be a product of any one of three processes: CO2-streaming, partial melting, or recrystallization of originally dry rocks. Here we suggest that these processes need not be independent and that they all may be related to the passage of melts through the crust.