College of Earth Sciences, Jilin University, Changchun 130061, China

Wengeng thrust fault in Langshan area of western Inner Mongolia developed at the northeastern boundary of Jurassic Wengeng sedimentary basin is a large thrust fault zone. The fault trends towards northwest, in which the hanging wall consists of Archean-Proterozoic metamorphic strata and Paleozoic plutonic intrusive body, and the footwall consists of Jurassic sediments, thrusting from northwest to southeast. The thrust fault cut and reformed the Early-Middle Jurassic sedimentary strata and is covered by the Early Cretaceous sedimentary strata, indicating that the thrust faultwas formed between the deposition of Early-Middle Jurassic Series and Guyang Formation. The research of fluid inclusion of syntectonic quartz veins in fault zone proves that the thrust faultwas formed in shallow structural level ranging from 5.5 km to 6 km, with temperature from 195�� to 210��, and the confining pressure from 50 MPa to 60 MPa. The macrostructure and microstructure of fault zone indicate the deformation of thrust fault wasmainly brittle.