Heterogeneity of water in garnets from UHP eclogites, eastern Dabieshan, China

Garnets in UHP eclogites from Bixiling in Dabieshan were investigated by Fourier transform infrared spectroscopy (FTIR). The results indicate that all gamets contain structural water that occurs as hydroxyl (OH-) and non-structural molecular water (H2O) possibly in the form of sub-microscopic fluid inclusions. The structural hydroxyl contents range from 92 to 1735 ppm (H2O WO and most are between 200 and 1000 ppm. Therefore, garnet in eclogite can recycle surface water into the mantle. Various water contents were observed among different samples of the same outcrop (similar to 150 m) and in different domains of the same sample (similar to 1 cm). This variability in structural H2O contents suggests that the mobility of fluids during UHP metamorphism was very limited, and that both subduction and exhumation processes of UHP rocks occurred in a short time interval. (c) 2005 Elsevier B.V. All rights reserved.