Petrology, Geochronology And Geotectonic Significance Of The Late Paleozoic Granites In Kangbao, North Hebei

Late Paleozoic granites of the North China Craton were taken to research in this researth, Eight different types of granites has been identified by geological observation in field, microscopic identification of outdoor areas. Meticulous work, such as EMPA test and zircon U-Pb dating,which has made the following understandings:(1) The mineral content of different granites were differently. Xi wufutang pluton, Xin cun pluton, Li shengbaogou pluton, San laohu pluton and Qian mengjiadi pluton, granite mafic minerals of which reduced in order. The size of the mineral grains from From the comparison to the small. The rock types were granodiorite- monzonitic granite- syenogranite. Xiao xigou pluton, Shi zhuliang pluton and Da pangou pluton, plagioclase of which were less and alkali feldspars increased in order. From syenogranites to alkali feldspar granites, structure of these granites were porphyritic-containing phenocrysts-porphyraceous.According to the EMPA test data, plagioclase(An = 39.6 ~ 43.4) should be feldspar in hornblende biotite granodiorites of the Xi wufutang pluton; plagioclase(An = 25.1 ~ 28.9) should belong to the oligoclase in hornblende biotite monzonite granites of the Xin cun pluton; plagioclase(An = 2.9 ~ 16.8) has the similar characteristics,which should be oligoclase and albite in monzonitic granite of the Li shengbaogou pluton. Plagioclase in granites from Da pangou pluton and Shi zhuliang pluton, were all albite(An = 0 ~ 1.6). Biotites in Xi wufutang pluton were mafic biotite and showed the characteristics of the crust-mantle mixed sources and granites in orogenic belt. Others pluton in kangbao,which were lepidomelane and showed the characteristics of crust sources, showed the characteristics of Alkaline granites. Hornblende amphiboles in Xi wufutang pluton were calcium [(Ca+Na) B≥1.00, NaB<0.50]. Further more, there were endenite, Magnesiohastinsite and hastingsite which also showed the characteristics of mixing with mantle material.(2) The results of the zircon Ti thermometer in granites showed that the average temperature of crystallization were higher than 750℃, which suggested that these granites and granodiorites were originated in the lower of the crust. Characterism of Elements, like Th, Zr, Hf and U showed that magma activities were in the open system when crystallization. As the same time, The multiphase fluid or magma added to the magma in that process.(3) Granites in Shi zhuliang pluton LA-ICP-MS zircon U-Pb age was 260.6 ± 1.6Ma; Xiao xigou pluton LA-ICP-MS zircon U-Pb age was 264.1 ± 1.7Ma; Qian mengjiadi pluton LA-ICP-MS zircon U-Pb age was 269.5 ± 2.7Ma; San laohu pluton LA-ICP-MS zircon U-Pb age was 276.3 ± 1.9Ma; Xin cun pluton LA-ICP-MS zircon U-Pb age was 280.4 ± 2.0Ma; Xi wufutang pluton LA-ICP-MS zircon U-Pb age was 284.7 ± 1.7Ma. Hornblende biotite granodiorites of the Xi wufutang pluton and hornblende biotite monzonite granites of the Xin cun pluton may form in the process of continental margin arc environment transforming to syn-collisional environment. other pluton,which contained alkaline granites and monzonitic granites, may be form from late syn-collisional environment to Post collision environment.