Amphibole-bearing migmatite in North Dabie, eastern China: Water-fluxed melting of the orogenic crust

• Amphiboles from the mesosome and leucosome in North Dabie have remarkable different REE compositions.
• Amphibole entrainment changes composition of the leucosome.
• Negative to positive Eu-anomalies of amphiboles may result from prolonged crystallization.

Amphibole-bearing migmatites from the North Dabie Zone in the Dabie Mountains were investigated in order to constrain the partial melting process. These migmatites are characterized by large euhedral poikilitic amphiboles with abundant inclusions of plagioclase, biotite, and quartz in leucosome and melanosome. The amphiboles show large variations in REE compositions, which is interpreted as the result of equilibration with different melts during melting and crystallization. Hornblende-plagiocase thermobarometry indicates that the migmatites formed at P-T conditions of ∼700–750 °C and 5 kbar, suggesting partial melting of a biotite + plagioclase + quartz-bearing protolith under water-fluxed conditions. The leucosomes range from tonalitic to granitic in composition having higher SiO2, Na2O, Sr, and Ba contents than the mesosome, but lower contents of CaO, FeO, MgO, TiO2, and MnO2. The granitic leucosomes are enriched in Ba, Rb, and K2O compared to the tonalitic leucosomes. The leucosomes have variable rare earth element patterns, which is attributed to different degrees of amphibole entrainment into the leucosome and feldspar fractionation during partial melting.