The micro-strain mechanism of Jiaochang arc structure in Songpan-Garze fold belt, northwestern Sichuan, China

The Jiaochang arc belt is characterized by synorogenic, multiphasic, coaxial compressional deformation and metamorphism, which is under the mid-shallow layer setting, and has some typical microtectonics, such as rotated helicitic structure, symmetric pres-sure shadow and kind structure etc. Based on 15 orientated samples′ microscopic features, dominant striking micro-strain feature of Jiaochang is symmetry, meanwhile magnitude of strain is roughly similar (γ≌1.8) in the western and eastern arc limbs, and percentage of compression is roughly equal (C≌27%) too. There is increasing tendency for micro-strain feature in the same unit from north to south, while there is decreasing tendency in different units, as well as the Flinn index (K1). The strain pattern is triaxial prolate strain. The symmetrically micro-structural feature in Jiaochang is significantly different to the unsymmetrical feature about "strike-slip" mechanism of arc belt, attributed to differential stress-strain mechanism controlled by the north to south main stress.