Extrusion tectonics inferred from fabric study of the Guanzizhen ophiolitic mélange belt in the West Qinling orogen, Central China

Abstract

The recently identified Guanzizhen ophiolitic mélange belt (GOMB) in the West Qinling orogen is regarded, by many geochemical and geochronological works, as the westward extension of the Shangdan belt in the East Qinling that separated the North and South China blocks. The GOMB trends generally NW–SE and comprises ophiolites and forearc volcanic–sedimentary complex (the Liziyuan Group). Ductile shear zones with various widths are a striking structural feature of the GOMB and studying them could contribute to a better understanding of the tectonic processes of the collisional orogeny in this area. Here we characterize the deformation style of these shear zones by combining the low-field anisotropy of magnetic susceptibility (AMS) data, microstructural and field observations. The new dataset demonstrates that the deformation of these ductile shear zones is dominated by dextral transpressional shearing under low amphibolite grade condition. Combining the dextral transpression of the GOMB and the coeval sinistral transpression of the Shangdan belt in the East Qinling, we propose a Late Triassic bilateral extrusion tectonics of the Qinling orogen in response to the collision between the Ordos and Sichuan blocks.