Neoproterozoic to Palaeozoic tectonic deformation history of the western Jiangnan Orogen, South China: Insights from new structural and geochronological data from northern Guangxi

Abstract

Recognition of deformation events documented in Neoproterozoic sedimentary sequences of the Jiangnan Orogen is critical in understanding the tectonic evolution of South China. In this contribution, we present new field based structural observations, microstructural analysis, and geochronological data for the Sibao and Danzhou groups in the southwestern Jiangnan Orogen of northern Guangxi, South China. Integrating the new information with previously published structural and geochronological data, we have identified three major deformation events. The earliest event generated E–W‐trending high‐angle tight linear and overturned isoclinal folds in the Sibao Group with their fold axial planes dipping to the south. This shortening event occurred in the mid‐Neoproterozoic time (840–800 Ma) and was associated with the orogenic collision between the Yangtze and Cathaysian blocks in South China. The angular unconformity between Sibao and Danzhou groups provides strong evidence for the collision. The second deformation event produced the large‐scale NNE–SSW‐striking ductile shear zones in the region. It also overprinted the pre‐existing E–W‐trending folds, refolded the Sibao Group, and generated the large‐scale NNE–SSW‐trending open folds in the overlying Danzhou Group and the west‐dipping cleavage within both groups. The second event occurred during the early Palaeozoic time (460–410 Ma) as a result of a WNW–ESE‐oriented intracontinental shortening process. The latest deformation event generated slight crenulation cleavage in the Sibao Group, some folds in the marble units of the Danzhou Group, and normal‐sense shearing along the pre‐existing NNE–SSW‐striking shear zones, all of which are the result of a NW–SE‐directed crustal extension during the late Palaeozoic (410–350 Ma) Kwangsian (Caledonian) orogenic collapse.