Abstract
Cordierite can contain variable amounts of H 2 O and CO 2 , and the total amount and relative proportions of these volatiles reflect the environment in which the cordierite was formed. In this study, cordierite has been experimentally equilibrated with a peraluminous granite melt, and the H 2 O contents of the phases have been determined by secondary-ion mass spectrometry (SIMS). The results show that cordierite can have a range of H 2 O contents at a single pressure and temperature, in this case 900 °C, 5.0 kbar. The maximum H 2 O contents occur at saturation, when H 2 O vapor is also present, at which point cordierite contains 1.69 ± 0.05 wt% and the melt contains 10.0 ± 0.42 wt%. However, as the system becomes progressively more water-undersaturated, the phases contain less H 2 O, and the partitioning coefficient ( D w = H 2 O Melt /H 2 O Cordierite , in wt%) decreases from 5.9 ± 0.3 to 4.4 ± 0.6. The experiments show that equilibration with a volatile-undersaturated melt provides an alternative to leakage as a mechanism for producing volatile-poor cordierites. Application of this experimental calibration to cordierites from granulite migmatites predicts that the melts with which they last equilibrated contained only 2.7–3.8 wt% H 2 O.
Published Version
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