This work deals with the preliminary relationship between strain path and strain partitioning pattern in a sinistral transpressional zone,Lancangjiang shear zone,located to the southeast of Tibet.Various ductile rocks provide an opportunity to investigate quantitative finite strain(Rs),kinematic vorticity values(Wm),and proportions of simple and pure shear components.The mean kinematic vorticity values(Wm) were evaluated based on three methods,such as Rs-θ,prophyroclast hyperbolic distribution method(PHD),and polar Mohr diagram construction(PMD).Wm for mylonitic metasediments of the low-grade schist belt ranged from 0.19 to 0.54.Protomylonites,mylonites,and ultramylonites recorded differential Wm values,0.19―0.73,0.11―0.8,and 0.84―0.95(even 0.99) respectively in the high-grade gneiss belt.Based on classical strain analysis and these kinematic vorticity evaluations,the shear zone is classified as a preliminarily bulk monoclinic symmetry.The pattern of vorticity path suggests that a previously undocumented transpressional setting and strain partitioning pattern in the southeast region of Tibet Plateau,characterized by steep-narrow domain of simple-shearing(Tertiary strike-slip shearing) deformation and wider domain of mostly pure-shearing(Tertiary contraction) to accommo-date intracontinental deformation.
The Xainza-Dinggye Normal Fault System (XDNFS) is a large-scale nearly-north-south trending exten-sional structure across central and southern Tibet. Its middle segment developed in Tethys Himalaya with features of earlier magmatic core complex and later normal faults dipping moderately to northwest-west. The magmatic core complex is made up by mylonitic leucogrante with a low-angle detachment fault on the top of it and overlain by lower-grade meta-sedimentary rocks. The structural pattern of the southern segment of XDNFS take the shape of a detachment fault dipping to southeast-east with the High-Himalayan rock series as the lower plate. The Southern Tibetan Detachment System (STDS) is expressed as a ductile shear zone composed of mylonitic leucogranite in the studied area of this note. STDS was cut by the later XDNFS, which presents that nearly-east-west striking STDS is not the controlling or adjusting structure of the nearly-north-south trending ex-tensional structures. The origin of
