Relationship between the crystallization of graphite and metamorphism of graphite-bearing granulite in Rizhuang, Jiaobei Terrane

The graphite-bearing pelitic granulite in the Rizhuang Town is located in the Laixi graphite metallogenic belt. Based on detailed studies of petrography, geochemistry, Raman spectroscopy and geochronology of the granulite, we considered it has undergone ultra-high temperature (UHT) metamorphism. The metamorphic evolution process of the granulite includes three stages although the mineral assemblage in the M-1 stage is not completely preserved. The mineral assemblages for the peak temperature stage M-2 and the post-peak stage M-3 are Grt + Qz + PI + Kfs + Sil + Rt + Liq and Grt + Qz + Bt + PI + Kfs + Sil + Rt + Liq, respectively. According to the phase equilibria modelling, combined with the two-feldspar geothermometers and the titanium-in-quartz geothermometers, we obtained the peak stage temperature and pressure conditions of the granulite variying at 1025 similar to 1100 degrees C and 1. 05 similar to 1. 2GPa. The Raman spectrum characteristics of the graphites in the studied samples show that most of them are highly crystallinity, which are consistent with the graphites formed under the metamorphic condition of granulite facies. The petrographic characteristics indicate that the high crystallinity graphite should crystallize during the transition from M-2 stage to M-3 stage. Age of the metamorphic zircons from the graphite-bearing granulite is similar to 1. 85Ga, which is a record of the cooling time after UHT peak metamorphism. The petrological and geochronological studies show that the formation and growth of high crystallinity graphite might closely relate to the regional anatexis event or the regional migmatization which occurs during the regional collisional event of the Jiao-Liao-Ji mobile belt.