Study Of The NNE Ductil Shear Zone In Tamusu Region Of Aixa Youqi, Inner Mongolia

A NNE-trending Ta mu su ductile shear zone was identified in Alxa Youqi, west inner Mongolia on the basis of 1:5000 regional geological survey. This ductile shear zone should be located within the magmatic of the north margin of North China Craton since Paleozoic.Ta mu su ductile shear zone was longth of about 9 km and width of 150 to 2500 m and strikes NNE with SE-dipping angle of 60~80°and sub-horizontal mineral lineations. Zoned characteristics are identified within this belt with strong to weak deformable from east to west. Structural Styles ,including folded mylonitic foliation, mineral lineation, S-C fabric, rotational porphyroclast,"domino"structure and"mica fish",indicate a NE-SW dextral strike-slip and west-directed thrusting.Estimation for P-T conditions,including mineral thermometer, EBSD fabric analysis for quartz, Two-feldspar Geothermometer suggest the temperature at 300~500°C and pressure at 250～400MPa for the mylonites. Thus, this ductile shear zone might occur at a metamorphic grade of green-schist facies and at middle-shallow tectonic level. The Values ofσ1-σ3 are estimated at 93.7～116.5 MPa using the way of dislocation density. Strain rate is 10-17 s-1(300℃) and 10-13 s-1(500℃).Shear strain of the mylonite and protomylonite calculated at 1.12 and 3.28 by S-C. Shear displacement of the mylonite and protomylonite zone are 1680m and 4920m. The kinematic vorticity are between 0.54 and 0.87 , which suggest that the deformation is not a strict simple shear but includes a component of pure shear.Geochronological result constraint the medium-high temperature ductile deformation initiated at ~256Ma.Combined with regional geological relationship, low temperature ductile deformation and brittle deformation are probably occurred in late Triassic and Cretaceous.