Preliminary study on age and genesis of Muzidian banded iron formation in the Dabie Orogen
The banded iron formation(BIF)is widely exposed in Muzidian area of Dabie Orogen,and its formation age and genesis have long lacked strong evidence support.Based on the detailed survey on Muzidian Formation sections in Wangjiafan and Liuzichong of Muzidian area,representative samples of garnet-amphibole-biotite-plagioclase gneiss,pla-gioamphibolite and magnetite-quartzite were collected to study zircon U-Pb geochronology and rock geochemistry,and to explore the formation age and genesis of Muzidian BIF.The results show that the diagenetic ages of garnet-amphibole-bio-tite-plagioclase gneiss and plagioamphibolite are(2 450±10)Ma and(2 469±17)Ma,respectively,the metamorphic age of(1 957±11)Ma is also recorded in the zircon of plagioamphibolite.The magnetite-quartzite samples have the characteristics of low Al2O3,TiO2,Na2O,K2O,low Zr,Th,Nb,REE and high Y/Ho ratio,and in the relevant genetic dis-crimination diagram,it shows that there is basically no supply of terrigenous clastic materials,but the participation of high-temperature hydrothermal fluid.Combined with previous data,it is believed that the Muzidian BIF was formed in the late Neoarchean-early Paleoproterozoic,and was formed by iron-bearing chemical deposition with high-temperature hydro-thermal participation and basically no terrigenous clastic materials.The Muzidian BIF is a typical Algoma-type BIF.
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