摘要
The Paleoproterozoic HP mafic granulite and calc-silicate were found from Laixi,Jiaobei terrane,consisting of almandine dominated garnet-augite-ferrohypersthene and grossular-zoisite-prehnite-albite respectively.Mineralogical and petrological studies show that the calc-silicate formed after the HP mafic granulite by processes combined retrogressive metamorphism with Ca alteration.The HP mafic granulites records four stage geological processes,including pre-granulite facies,peak granulite facies,retrogressive combined with Ca alteration and complete Ca alteration processes with mineral assemblages as Cpx + Pl + Qtz (M 1),Grt + Cpx + Rt + Qtz (M 2),Cpx + Pl + Opx + Ilm + Mgt + Ep (M 3) and Grs + Zo + Prh + Ab + Cal (M 4).The HP mafic granulite is rich in LIL elements Ba,Rb,K,Rb,Th and depleted in HFS elements Nb,Zr,Ti and Y,having LREE rich right-inclined REE pattern and showing island-arc basaltic characteristics.Further studies by using discrimination diagrams,the HP mafic granulite presents island-arc tholeiitic characteristics,probably formed in the back-arc extension tectonic setting.After formation of the mafic rock,it experienced granulitic facies metamorphism during collisional convergence of the Jiao-Liao-Ji orogenic belt and afterwards experienced retrogressive and Ca alteration processes during the lift of the belt.