The deformation and mechanisms of the Zhangbaling tectonic belt during Indosinian to early Yanshanian: Implications for the relationship with the Tan-Lu Fault Zone

The Zhangbaling tectonic belt is located in the middle segment of Dabie-Sulu Orogenic Belt and in the eastern part of the main segment of the Tan-Lu Fault Zone (TLFZ). Based on detailed field work and comprehensive analysis, this study discussed the tectonic evolution mechanics of the Zhangbaling tectonic belt and the Tan-Lu Fault Zone as well as the relationship between them during Indosinian to early Yanshanian period. Three stages of tectonic deformation have been determined in the period from Indosinian to early Yanshanian in Zhangbaling area, i.e., a series of WNW and nearly EW trending tight congruous nearly recumbent folds formed in the early stage; a flatly ductile shearing zone formed mainly between Beijiangjun lithofm. and Xileng lithofm. in the middle stage and the demonstrate NNE trending wide flat folds and strong thrusting or napping from NW to SE formed in the last stage. The superimposition of these three deformation stages formed the basic tectonic framework of this area. The folding and thrusting (sliding in the front margin) was developed in the mid-upper crust (include sedimentary cover) during the period of subduction and collision processes between South China Block and North China Block, shows a progress deformation of the three stages during the period of Indosinian and early Yanshannian due to the conversion of the Tethyan to the Circle Pacific Ocean tectonic regimes. The Tan-Lu Fault Zone can be divided into two big development phases since Hercynian. The first phase is a fault zone sensu lato, as a boundary of a rifted cratonic margin (or basin) that shows a wide arc-shaped along the northeastern margin of the South China Block during Indosinian. The TLFZ of this period is a collision suture between South China Block and North China Block during Indosinian period, a thrust-napping fault zone belong to the Tethyan regimes sensu lato, as well as the southeast margin of the Zhangbaling tectonic belt. This big phase corresponds to the three stages deformation activities in Zhangbaling area. The second phase is a wrench fault system usually mentioned by most researchers, which belongs to the Pacific Ocean Cycle Regime sensu stricto since early Yanshanian to Himalayan periods.