Lithology and Protolith of HP-UHP Eclogite Facies Metamorphic Rocks and Relevant Rocks of the Changpu-Bixiling Area, Dabie Mountains

Two NNW-trending HP-UHP belts are found in the Changpu-Bixiling area, Yuexi County, Anhui Province, The western belt from Tuqiaochong to the Changpu Hydropower Station consists mainly of banded jadeite quartzite and marble with minor quartz-bearing dark eclogite and light-coloured eclogite, and the eastern one from Xiaolanshanling to Bixiling, banded light-coloured eclogite series and dark-coloured eclogite series. The two eclogite series in the area are different in their rock associations, mineral assemblages and mineral com-positions. The light-coloured eclogite is interbanded with jadeitic omphacite quartzite, kyanite-rich rock, gar-netite and jadeite-garnet-white mica schist. The light-coloured eclogite contains jadeitic omphacite (Jd 65~45) + garnet (Pyr + Gro,60 ± ) + kyanite ± phengite ± quartz, with secondary amphibole and epidotite; whereas the dark-coloured eclogite is composed of omphacite (Jd 20~50) + almandine-rich garnet(Alm 50~ 60)+ rutile ±quartz, with secondary amphibole, and the quartz dark-coloured eclogite, omphacite(Jd 40-45) + pyrope-rich garnet(Pyrl0-30)+ quartz + rutile, with secondary amphibole and feldspar. In the field, the dark-coloured eclogite is closely associated with garnet peridotite. The protolith of the light-coloured eclogite is basic tuffaceous sediments, and those of the associated jadeite quartzite, jadeitite and white mica schist are silt-stone, feldspar sandstone and muddy siltstone respectively. The protolith of the dark-coloured eclogite is basic tuffaceous lava. The protolith of marble is limestone. Besides, the chemical compositions of garnet and om-phacite in eclogite facies rocks evidently depend on their protoliths under the same metamorphic conditions.