Transpression in the Eastern Jiangnan Orogen and its implications for ductile deformation process and regional Tectonics of the South China block

Abstract

The transpressive deformation in the eastern Jiangnan Orogen during the Early Paleozoic is the structural response to the oblique convergence of the Yangtze-Cathaysia blocks, and this relationship is critical for understanding the tectonics of South China. The Jiangwan–Huangshan shear zone (JHSZ) and Baiji–Sanyang shear zone (BSSZ) exhibit NEE–SSW-trending oblique dextral and sinistral shearing, respectively, and their evolution resulted in local E–W dextral strike-slip shearing. Most kinematic vorticity values range from 0.4 to 0.81, which implies that the JHSZ and BSSZ deformed under the contribution of both pure-shear and simple-shear components, suggesting complicated deformation histories for those orogenic shear zones. The quartz and feldspar deformation mechanisms, opening angles and lattice preferred orientation (LPO) patterns of the quartz c-axis fabrics suggest shear deformation temperatures between 400 and 550 °C in the eastern Jiangnan Orogen. Locally deformation occurred under high-temperature (>600 °C) conditions. Combined with previous data and regional geology, these findings indicate that the shearing deformation in the eastern Jiangnan Orogen accommodated the oblique convergence between the Yangtze and Cathaysia blocks during the Early Paleozoic, which was possibly caused by the final assembly of Gondwana.