Transformation from Neoproterozoic Sinistral to Early Paleozoic Dextral Shearing for the Jingdezhen Ductile Shear Zone in the Jiangnan Orogen, South China

Abstract

The Jingdezhen ductile shear zone is evolved from the Neoproterozoic Zhangyuan ophiolite melange belt in the eastern Jiangnan Orogen, South China. Comprehensive study of geometry, kinematics, quartz c-axis fabric, temperature-pressure conditions and geochronology were conducted in this study. The Jingdezhen shear zone extends ∼180 km along the NE orientation with two groups of subvertical foliation and subhorizontal lineation. One group of foliation strikes NEN orientation whereas another one NEE orientation. Field investigation, microscopic observation and quartz c-axis fabric show that sinistral shearing along NEN-striking foliation occurred earlier than dextral shearing along NEE-striking foliation. Syn-tectonic staurolite porphyroblasts and deformation manner of feldspar imply that sinistral shearing occurred at 530–420 oC and 6–2 kbar. Deformation manner and c-axis fabric of quartz and pre-tectonic staurolite porphyroblasts indicate that dextral shearing took place at 420–300 oC. LA-ICP-MS zircon U-Pb and mica 40Ar/39Ar dating indicate that the sinistral shearing occurred during Neoproterozoic orogeny (830–800 Ma) whereas the dextral shearing at 447±12 Ma. The sinistral shearing resulted from the Neoproterozoic final assembly between the Yangtze and Cathaysia blocks. The dextral shearing was caused by Early Paleozoic orogen parallel extension and clockwise rotation.