Heterogeneity of water in UHP eclogites from Bixiling in Dabieshan: Evidence from garnet

Garnets in ultrahigh pressure (UHP) eclogites from Bixiling in Dabieshan were investigated by Fourier transform infrared spectrometer (FTIR). The results demonstrate that all garnets contain structural water which occurs as hydroxyl (OH), with contents ranging from 164 to 2034 ppm (H2O wt.) and mostly higher than 500 ppm. Like omphacite which is another major OH-rich mineral in eclogites, garnet is an important carrier that can recycle the surface water into deep mantles. Heterogeneity of water in garnets exists not only among different samples of the same outcrop (～150m), but also among different crystals of the same sample (～1cm). This indicates that the mobility of fluids during UHP metamorphism is very limited (possibly on centimeter scales), and that both subduction and exhumation processes of UHP rocks are very fast.