Fluid-absent melting versus CO2 streaming during the formation of pelitic granulites: A review of insights from the cordierite fl uid monitor

An extensive database of published cordierite volatile contents from twenty-eight different high-grade terranes is used to investigate whether CO2 streaming or fl uidabsent melting processes prevail during the formation and evolution of granulites. In most case studies the cordierite volatile contents, calculated activities, and melt-H2 O contents are entirely consistent with a mode of origin dominated by fl uid-absent melting processes. In accordance with published experimental and theoretical evidence these data suggest that CO2 is not a prerequisite for granulite formation. Even in cases in which cordierite preserves high CO2 contents this does not necessarily imply that fl uid-saturated conditions prevailed. A cordierite may be CO2 -rich but can still be fl uid undersaturated and preserve H2 O contents that equilibrated with melts formed from fl uid-absent melting. In fl uid-saturated case studies the mechanism and relative timing of saturation should be evaluated. It is evident from the data that most fl uidsaturated granulites formed initially under fl uid-absent conditions but subsequently became fl uid saturated along a retrograde path. © 2011 Geological Society of America.