摘要
///The khondalite series in Helanshan region is a main part of the khondalite belt in the western block of the North China Craton.Recently,high pressure pelitic granulite with typical mineral assemblage of garnet+kyanite+perthite were discovered in the Helanshan khondalite series.Petrographic observation and phase modeling indicate that the pelitic granulite experienced four stages of metamorphism.An early prograde metamorphic stage（M1）was recognized from inclusions of biotite and muscovite in garnet.The peak metamorphic stage（M2）is characterized by the presence of garnet+kyanite+perthite,with a probable PT condition of 1.4~1.5 GPa at ca.850~870 ℃.The post-peak decompression（M3）is indicative of an isothermally overprinting of sillimanite and cordierite from kyanite and garnet with pressures of 0.6~0.8 GPa at ca.840~860 ℃.Development of most biotite suggested a late-stage retrogression（M4）under PT conditions of 780~810℃,0.45~0.55 GPa.This clock-wise P-T path,is consistent with a thinning process of thickened continental crust which may be a result of the collision between the Yinshan block and Ordos block.