| Bounded by Shangdan Suture Zone (SSZ), the Qinling Orogen is divided into North Qinling Belt (NQB) and South Qinling Belt (SQB). The Forearc Sedimentary Unit (FSU), which is bordered SSZ to the north and seperated from Liuling Group by Mianyuzui-Maanqiao Ductile Shear Zone to the south, is embedded into NQB like a prism. The detrital zircons of meta-conglomerate shows the provenances are all from NQB, which implies FSU is belonged to NQB. The Petrographic and Geochemical evidence shows that, rocks of FSU were formed in an active Continental Margin. FSU was probably connected with the over island arc of the NQB. Therefore, FSU is included into NQB in this research.FSU is mainly developed a suit of parablastesis. Recently, many researchers studied its Geochronology, Isotope-Geochemistry and provenances thoroughly and got new ideas. But, when it comes to the deformation and phase, people have little research. Neighbored with SSZ, rocks from this zone have important meanings to the further research of deformation.By detailed recorded occurrence of foliation and lineation, study of structure style, combined with the basis of previous research, we collate and stipulate two phases of deformation from the subduction to the collision:the early the thrust-nappe, subducted ductile shear and the late the sinistral ductile shear. The earlier phase shows S-dipping transposition foliation and W-dipping dip-lineation, and tight folds; While the later, performs as penetratively developed mylonite belt and the resulting horizontal mineral stretching lineations. Combined with the previous research, we deduce that the earlier phase was the result of the Qinling Ocean NW-ward subducting; the later phase was caused by sinistral ductile shear between the North China Block and the South China Block.Combined with the youngest age of three detrital zircon samples(420Ma) and the oldest mafic dyke(410Ma), we limit the age of the sinistral deformation at 420-410Ma. |
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