PETROLOGY AND GEOCHEMISTRY OF LATE PALAEOZOIC GRANITOIDS IN NORTH MARGIN OF THE NORTH CHINA PLATE

The granitoids of late Palaeozoic in north margin of the north China plate are divided into four periods according to geological character and geochemistry . Devonian granitoids assemblage mainly including quartz monzonite, amphibole monzonite and quartz diorite. The petrological geochemistry characteristics indicate that they are the typical I-type and adakitic rocks which belong to metaluminous and high-K calc-alkaline series, poor potassium and rich sodium, and are rich in large ion lithophile elements but depleted in high strength field elements. They are show a LREE-enriched pattern, and the Eu shows weak positive anomaly.

Carboniferous granitoids belongs to high-K calc-alkaline series are I-type and adakitic-like granodiorites which proceed from metaluminous to peraluminous, for the enrichment of Rb,Ba,Sr,Th,U,Nd and Zr and relative depletion of Cd,Ni, and poor in NbATi. They are show a LREE-enriched pattern but no pronounced Eu anomaly,

Permian granitoids can be breaked into two intrusion periods . The early Permian granitoids were made up of biotite granites and monzonitic granites. They belong to metaluminous to peraluminous and calc-alkaline to high-K calc-alkaline series. The trace elements are characterized by high concentrations of large ion lithophile elements(LIL) and depletion of Nd,Ta,Ti,Tb and Y.The LREE are strongly enrichment and Eu shows light negatively anomaly to no anomaly. The middle-late Permian granitoids are characterized by Si, Al and alkalis enrichment, belonging to metaluminous- peraluminous and calc-alkaline to high-K calc-alkaline series. Trace elements show that high concentrations of Rb, Ba,Th,U,Nb,Ta and depletion of Sr,Ti and Y. The LREE are strongly enrichment, Eu shows light negatively anomaly.

The Devonian and middle-late Permian granitoids were mainly composed by alkaline granitoids which represent post-collisional orogeny. The early Carboniferous and early Permian granitoids mainly consist of mid-acidic granitoids which were possibly derived from a mantle-crust mixing, and indicated the syn-collision tectonic setting.