Syn-Faulting Calcite Ages:Constraint for the Late Mesozoic Deformation of the Ningzhen Mountain,Eastern China

It is difficult to date a brittle fault because of the absence of effective dating methods.Recently,calcite U-Pb dating has drawn the attention of many researchers and has been successfully applied to constrain the age of brittle deformation.The South China Block(SCB)has experienced multiphase deformations characterized by widespread brittle faults and folds,which has led to significant debate on the Mesozoic dynamic mechanism and deformational phases.A syn-faulting calcite vein that occurred in the Permian limestones of the Ningzhen Mountain region was analyzed using U-Pb dating and geochemistry techniques in this paper.The U-Pb dating results display multiphase activities with two mixed ages of 109.9±5.8 Ma(MSWD=46,n=231)and 117.2±2.4 Ma(MSWD=3.6,n=150).The age of 117.2±2.4 Ma likely represents the timing of the brittle faults.Trace elements and rare earth elements data indicate that these fault-related calcites are mainly derived from host limestones and unrelated to Cretaceous magmatic activity.These faults formed in a tectonic reactive period and dormant time of the adakitic magma in the Lower Yangtze region.