Strain, Kinematic Vorticity Analysis And Ductile Thinning Of Sonid Zuoqi Metamorphic Core Complex Ductile Shear Zone, Inner Monglia

Sonid Zuoqi ductile shear zone of metamorphic core complex which is located in the south margin of Central Asian Orogenic Belt, is a low angel, strike to WN and dips to SE shear zone. Based on the rate of protolith and matrix,we can conclude that the rock within the shear zone is mylonite. The Mesoscopic features of the shear zone are characterized by well-developed mylonitic foliation and stretching lineation; the Microscopic features include recrystallized quartz belt, feldspars porphyroclasts and muscovite fish. The mylonites within the shear zone are widespreadly fine grained, and show many quartz recrystallization, feldspars porphyroclasts and mantle-core structure. The shear indicators, such as asymmetric porphyroclasts, S-C fabrics, and shear bands, suggest consistent top-to-the-SW shearing.Finite strain measurement using feldspars grains of mylonite show the Flinn parameter(K), the natural strain(γ), Lode’s parameter(υ) and the strain intensity(Es) ranged from 0.55-1.36,1.97-3.03,-0.15-0.34 and 0.56-0.98, respectively. The logarithmic Flinn diagram indicates that the strain type of the mylonites was constriction to plane strain during the formation of mylonites foliation and lineation. The kinematic vorticity estimated by Polar Mohr shows kinematic vorticity values ranged from 0.70 to 0.95, which suggest that the Sonid Zuoqi ductile shear zone of metamorphic core complex experienced simple shear-dominated general shear during the formation of the mylonitic foliation and lineation. The kinematic vorticity values(0.70-0.95) indicate there are the thickness changing perpendicular to the shear zone, based on the three-dimensional finite strain and kinematic vorticity, we estimated the ductile thinning changed from 62% to 86%, with an average of 75%. The finite strain measurement shows the X axis elongate continuously, the Y axis remain unchanged and the Z axis shorten continuously, together with kinematic vorticity values, which indicated the shear type of Sonid Zuoqi ductile shear zone of metamorphic core complex is a elongateing-thinning shear zone.