Petrographical Characteristics And P-T Calculations Of The Granulites From Liangcheng,Inner Mongolia And Datong,Shanxi

The granulite provides plenty information of mid-lower crust of the earth.Most of granulites in China are found in North China Craton.As we know,mafic and pelitic granulites coexist in space and come into being almost simultaneously in Liangcheng,Inner Mongolia and Datong,Shanxi,which belong to the same tectonic belt.It is in debate whether the granulite in Datong-Liangcheng area is high-pressure granulite.In this paper selects the mafic and pelitic granulites of Datong-Liangcheng for research,because the two areas are very close,and the mafic and pelitic granulites are spatially in company of others.By comparing the same rocks in different areas,the peak metamorphic conditions of granulite can be more limited and the geological significance can be explained.According to the petrographic observation,traditional mineral thermometers and THERMOCALC phase equilibrium modeling were used to calculate the temperature and pressure of granulite in Liangcheng area of Inner Mongolia.The results show that the peak mineral assemblage of mafic granulite in Liangcheng is g+cpx+pl+ilm,and the peak metamorphism condition is 11.47-13.07 ±1.90kbar/739.4-770.7 ?,indicating high pressure granulite facies;the post peak decompression stage is g+cpx+opx+pl+ilm,indicating medium pressure granulite facies.The peak mineral assemblage of pelitic granulite in Liangcheng is ksp+g+ilm+sp+liq+q+sill,and the post peak decompression stage is ksp+g+ilm+sp+cd+q+sill,suggesting the metamorphic conditions of5.3-5.7kbar/835-900 ?.According to the petrographic observation,the pre-peak mineral assemblage of pelitic granulite in Datong is Grt+Bt+Kfs+Qtz+Rt,showing the metamorphic temperature is 773-880 ? by using Zr-in-rutile thermometry;The peak mineral assemblage of pelitic granulite in Datong is Grt + Sil + Kfs + Qtz;The post peak mineral assemblage of pelitic granulite in Datong is Grt+Bt+Ms+Qtz,showing the temperature and pressure is 3.8-4.4kbar/576-589 ? by using garnet geobarometer.Therefore,we draw two conclusions are following:(1)The metamorphiccondition of mafic granulite in Liangcheng,Inner Mongolia is11.47-13.07kbar/739.4-770.7?,indicating high pressure granulite;the metamorphic condition of the post peak decompression stage of pelitic granulite is5.3-5.7kbar/835-900?,indicating lower in pressure and higher in temperature than that of previous studies,but has not reached ultrahigh temperature metamorphism.(2)The pre-peak metamorphism temperature of pelitic granulite in Datong is 773-880?,the degree of metamorphism in the two areas is consistent with previous studies.