| As the most representative and complex Paleoproterozoic orogenic/mobile belt in the North China Craton(NCC),the Jiao-Liao-Ji Tectonic Belt(JLJTB)has undergone multi-stage magmatic-metamorphic and tectonic deformation events.However,the tectonic nature and evolutional history of the belt have still remain controversial.Paleoproterozoic granitoid rocks form an important component of the JLJTB throughout all of its evolutionary stages.Granitoid rocks formed during different evolutional stages recorded the tectonic evolution of the tectonic belt.The determinations of their sources and petrogenesis can provide important constraints on deep material composition,tectonic nature and evolution.In this study,to define the emplacement and metamorphic ages,sources and petrogenesis of the Paleoproterozoic striated and gnessic granitoid rocks,and further constrain the tectonic nature and evolutionary history of the JLJTB,integrated all-rock geochemistry,zircon LA-ICP-MS U-Th-Pb and Lu-Hf isotopic analyses have been conducted,combined with published data and geological evidences,the main conclusions have been achieved as follows:1.Paleoproterozoic striated and gnessic granitoids are widely distributed in the eastern Liaoning Province,and mainly comprise striated magnetite,hornblende and biotite-bearing monzogranitic gneiss,light hornblende and biotite-bearing granitic gneiss and weakly gneissic biotite-bearing monzogranitic gneiss2.The in situ LA-ICP-MS zircon U-Th-Pb analyses in combination with CL images of zircon morphology and internal structure,and REE indicate that the Paleoproterozoic emplacements were mainly taken place during 2180-2160 Ma,whereas one sample gave an emplacement age of2330 Ma,and experienced metamorphism at-?1.89 Ga.3.All-rock geochemistry analysis shows that They have high SiO2(71.68?76.38 wt%),Fe2O3+FeO(1.61?4.35 wt%)and total alkali(K2O+Na2O=7.57?9.3 wt%)with K2O/Na2O>1,and low CaO(0.2?1.6 wt%),MgO(0.05?0.24 wt%,Mg#=3.82?12.96),P2O5(0.01-0.06 wt%)and TiO2(0.12?0.4 wt%)contents;They have relatively high REEs contents(LREE=104?440 ppm),enrichment in light REE and depletion in heavy REE with((La/Yb)n ratios of 2?11,and strongly negative Eu anomalies(Eu/Eu*=0,30?1.18,average of 0.56).These samples show low Sr content(mostly<100 ppm),Rb(62.8?187 ppm),Cr and Ni contents,buthigh Zr(>250 ppm),Yb(>2 ppm)and Zr+Nb+Ce+Y(average=506 ppm)contents,and 10000*Ga/Al values of larger than 2.7.In primitive mantle normalized trace element spider diagrams,they exhibit strong enrichments in Rb,U,K,Zr and Hf,but depletion in Nb,Ta,Sr and Ti.They are ferroan,alkali-calcic to calc-alkalic and metaluminous-weakly peraluminous,belong to A2-type granite with the zircon saturation temperature>800 eC4.Igneous zircons of the Paleoproterozoic granitoids have I76Hf/177Hf ratios ranging from 0.280904 to 0.282233,positive and negative ?Hf(t)values of-17.4?+11.7,and depleted mantle two-stage model ages varying from 2304?4526 Ma with an average of 2817 Ma,indicating sources of ancient crustal materials with some juvenile crust.5.The analyses of all-rock geochemistry and zircon Hf isotopes of the Paleoproterozoic striated and gnessic granitoids suggest that the Paleoproterozoic granitoids were derived from partial melting of continental crust(TTG rocks)under high temperature and low pressure extension setting related to up-welling of mantle magma.6.The results of this study combined with other published data and evidences suggest that the JLJTB might experience tectonic evolutionary history of multi-stage extensions,formation of initial ocean basin,ocean-continent subduction to continent(arc)-continent collision followed by extension in Paleoproterozoic. |
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