Mineral inclusions in zircon from gneisses in the ultrahigh-pressure zone of the Dabie mountains, China

Mineral inclusions in zircon from gneisses in the ultrahigh-pressure (UHP) zone of the Dabie Mountains, China, are studied by using laser Raman spectrophotometry. We identified numerous mineral inclusions including coesite, quartz, clinopyroxene, phengite, barite, anhydrite, and feldspar. Coesite is found to occur as zircon-hosted inclusions in all types of gneisses, indicating that these gneisses had shared the ultrahigh-pressure metamorphic history with the UHP eclogite blocks that reside in them. The occurrence of barite and anhydrite probably implies the existence of SO₄^-2-bearing fluids during the UHP metamorphic stage. We also found no simple ways to correlate growth zones of zircon as shown by cathodoluminescence images with metamorphic conditions determined from inclusion in any specific zircon grains. Of particular interest is the discovery of coesite included in zircons from gneiss of the "cold" eclogite zone that was previously considered to have not experienced UHP conditions.