Sinistral transpressive deformation in the northern part of Zhangbaling uplift in the Tan-Lu fault zone and its ~(40)Ar/~(39)Ar dating.
Zhang Qing1, Zhu Guang2, Liu Guosheng2 , C.Teyssier1, W.J.Dunlap3 1.Department of Geology and Geophysics, University of Minnesota, Minneapolis MN55455, USA2.College of Resource and Environment Engineering, Hefei University of Technology, Hefei 230009, China3.Research School of Earth Sciences, Australian National University, Acton, ACT 0200,Australia
Ductile detachment deformation belt, brittle-ductile transition belt and brittle foreland fold-fault belt are exposed on the northern part of Zhangbaling uplift in the Tan-Lu fault zone from west to east. The Zhangbaling schists in the ductile detachment deformation belt are widely mylonitized under low greenschist facies. The belt shows gentle mylonitic foliation and nearly N-S trending mineral elongation lineation. Analyses of microstructures and quartz C-axis fabrics demonstrate that the ductile detachment belt has experienced top-to-south motion. The deformation motion changes into top-to-SSE then top-to-SE thrusting, showing a sinistral transpressive deformation zone. The ductile deformation belt exposed in the Zhangbaling group is a detachment deformation belt between deeper, steep strike-slip structures and shallower, brittle structures. The differential deformation between the different levels caused top-to-south shear motion under a general northward movement of the fault block. 40Ar/39Ar dating of muscovite separated from the Zhangbaling schists with different grain sizes indicates that the deformation took place in a range from (236.2±0.5) Ma to (238.0±0.4) Ma, i.e. the latest Middle Triassic. It is suggested that the sinistral displacement of the Tan-Lu fault zone happened in a continental, deep subduction stage of the North and South China plate collision, and was derived from intracontinental transform faulting.