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The high–temperature and high–pressure experiment on natural block rock indicates that dehydration–melting of hydrous biotite (Bi) and partial melting of felsic minerals in garnet–biotite–plagioclase gneiss are mainly controlled by temperature, while mineral phase transformation is not only controlled by temperature–pressure conditions but also genetically associated with hydrous mineral dehydration–melting and partial melting of felsic minerals. According to the characteristics of biotite dehydration–melting and garnet transformation reaction, three stages may be distinguished: (1) when the experimental temperature is 700°C, biotite transforms to ilmenite (Ilm) + magnetite (Mt) + H2O and garnet to magnetite (Mt); (2) when the temperature is 730–760°C, biotite is dehydrated and melted and transformed into K2O—rich melt + Ilm + Mt, and garnet, into hypersthene (Hy) + cordierite (Crd); (2) when the temperature is up to or higher than 790°C, biotite is dehydrated and melted and transformed into melt + Hy + Ilm + Mt, and garnet, into the hypersthene (Hy) + spinel (Sp) + cordierite (Crd) assemblage. The melt proportion and its evolutionary characteristics are mainly controlled by dehydration–melting of hydrous minerals and partial melting of felsic minerals besides P–T conditions; In addition to the traditional solid + solid (or fluid) reaction and dehydration—melting reaction, the metamorphic reaction involving melts (reaction between unmelted minerals and melts) is one of the most important reactions in granulite facies metamorphism and its attendant remelting (or regional migmatization). This experiment may provide dependable experimental data for an in–depth study of the genetic mechanism of mineral assemblage evolution and its geological dynamic significance in granulite facies metamorphism of the studied area.

The early Precambrian khondalite series is widely distributed in the Jining-Zhuozi-Fengzhen-Liangcheng area, southeastern Inner Mongolia. The khondalite series mainly consists of sillimanite garnet potash feldspar (or two-feldspar) gneiss and garnet biotite plagioclase gneiss. These gneissic rocks have commonly experienced granulite-facies metamorphism. In zircons separated from sillimanite garnet potash feldspar gneisses, many mineral inclusions, including Sil, Grt, Ky, Kfs, Qtz and Ap, have been identified by the Laser Raman spectroscopy. Generally, prograde metamorphic mineral inclusion assemblages such as Ky + Kfs + Qtz + Ap and Ky + Grt + Kfs + Qtz are preserved in the core of zircon, while peak granulite-facies metamorphic minerals including Sil + Grt + Kfs + Qtz and Sil + Grt + Kfs + Qtz + Ap are identified in the mantle and rim of the same zircon. However, in some zircons are only preserved the peak metamorphic minerals such as Sil + Grt + Kfs + Qtz and Sil + Grt + Kfs + Qtz + Ap from core to rim, and in others are inherited the primary cores with minor mineral inclusions of Kfs + Qtz, with peak metamorphic mineral inclusions around the inherited cores. These data indicate that the mineral assemblage evolution of sillimanite garnet potash feldspar gneisses in the study are did experience a polymorphic transformation of kyanite to sillimanite. In garnet biotite plagioclase gneisses, secondary electron microscopic images reveal that most zircons display distinct zoning textures, which comprise cores and rims, each with distinctive inclusion assemblages. The inherited mineral inclusions, mainly consisting of Kfs + Pl + Qtz, Kfs + Qtz and Kfs + Qtz + Ap, are preserved in the primary cores, while peak granulite-facies mineral asemblages, including Grt + Bt + Pl + Qtz + Ap, Grt + Bt + Pl + Qtz and Grt + Bt + Pl + Qtz + Rt, are identified on the rims. The occurrence of peak metamorphic mineral inclusions in zircons indicates that these gneissic rocks, including sillimanite garnet potash feldspar gneiss and garnet biotite plagioclase gneiss, have experienced granulite-facies metamorphism. Secondary electron microscopic images of zircons from the khondalite series display distinct zoning from core to rim, and are genetically related to the primary, prograde, and peak metamorphic mineral inclusion assemblages respectively. These images reveal irregular zoning patterns and varying thickness of cores and rims. The abundance of inclusions complicates the conventional U-Pb age dating. Therefore, the SHRIMP micro-spot U-Pb method is essential for the protolith and metamorphic age dating of the khondalite series, southeastern Inner Mongolia.