Flow vorticity in Zhangbaling transpressional attachment zone, SE China

Plagioclase porphyroclasts with well-preserved idiomorphic shapes and zoning, and showing limited clast interaction, are ubiquitous in the flat-lying Zhangbaling schist that is exposed east of the Tan-Lu fault in southeast China. Plagioclase porphyroclasts define rigid particles whose distribution be related to the kinematic vorticity of the schist using the methods of porphyroclast hyperbolic distribution (PHD) and modified Rf/ϕ (Passchier/Wallis plot). The kinematic vorticity numbers calculated from this approach range from Wk = 0.72 to 0.82, increasing progressively from south to north along the Zhangbaling belt. Such a Wk distribution indicates that the Zhangbaling schist was deformed uniformly under simple-shear dominated general shear, and that the Zhangbaling ductile crust experienced relatively even crustal thinning deformation. The subhorizontal Zhangbaling schist is considered a mid-crustal attachment zone that coupled the rigid upper crust to a subvertical, wrench shear zone in the lower crust.

► The Zhangbaling schist was produced in simple-shear dominated general shear. ► The Zhangbaling ductile midcrust experienced fairly uniform deformation. ► The ductile crust underwent relatively even crustal thinning. ► The Zhangbaling schist is considered a midcrustal attachment zone.