Identification And Petrogenesis Of Paleoproterozoic Syn-collisional Granites From Huai'an Complex,North China Craton

Though the timing of final cratonization of the North China Craton?NCC?was constrained in the range of 2000¹800Ma,the peak collisional timing is still a controversy of 1900Ma,or 1850Ma.Recently,potassic biotite-granites were recognized from the Huai'an Complex,north-central of the North China Craton.Detailed study on their emplacement age,petrogenesis and tectonic settings can provide important clues to gain insights into the crust evolution and the final cratonization of the NCC.Zircon U-Pb dating and whole-rock geochemical analysis were carried out to put constraints on their formation age and petrogenesis.The major results and conclusions are exhibit as follows:1.Two biotite-granites samples yield upper intercept ages of 1924±33?MSWD=15?and 1931±61Ma?MSWD=0.52?,respectively,representing the emplacement age,similar to the metamorphic age of mafic high-pressure granulite in the same area and those of the S-type granites in the khondalite belt.Those consistent formation ages indicate that the biotite-granites were generated in a syn-collisional tectonic setting.2.The biotite-granites exhibit high K₂O/Na₂O ratios?1.04².06?,subaluminous.They exhibit prominent positive Eu anomalies with high La/Yb,whereas they are enriched by LILE?such as Rb,Sr,Ba?and LREE,and depleted in HFSE?such as Nb,Y,Ta?and HREE.As Eu/Eu*ratio increased,the concentrations of Sr,Ba,Ca are also elevated,but Rb,Th,Y elements and?REE abundance are decreased,which can be attributed to accumulation of plagioclase and differentiation of those associated minerals,etc.monazite,allanite and apatite.3.Zircon saturation temperature range of potassic granites is from 683 to 813?,average value is 726?;Titanium-in-zircon thermometry shows from 712 to 816?,average value is 753?;Calculation of oxygen fugacity shows that?FMQ value is between-4.7 and 10,average value is 0.6.The consolidation P-T of biotite-granites are estimated at 700?and 2kbar,and the source rocks in the low crust are>10kbar.4.The biotite-granites were generated by re-melting of TTG rocks in the lower crust under syn-collisional tectonic setting,and the peak timing of collision can be constrained before 1.93 Ga.