PERVASIVE REMAGNETIZATION OF PALEOZOIC ROCKS ACQUIRED AT THE TIME OF MESOZOIC FOLDING IN THE SOUTH CHINA BLOCK

A total of 152 paleomagnetic samples was collected from 23 sites distributed over six Paleozoic formations, with ages ranging between Middle Ordovician and Early Permian, in the Tangshan type section in the Nanjing area of South China. Stepwise thermal demagnetization has successfully resolved two magnetization components from these samples. Component A with northerly shallow tilt-corrected directions resides in approximately 95% of the total number of samples analyzed; this component passes fold tests at the 99% significance level in three formations. The overall mean direction of component A is 350/-3 (tilt-corrected, a95=7.2) Component B, isolated from 19 samples in two formations (C1 and D3), yields negative fold tests at the 95% significance level and is, therefore, younger than the Mesozoic folding. The overall site mean direction of component B is 354/-4 (in situ, a95=8.4). The tilt-corrected direction of component A clearly resembles the in situ direction of component B, indicating that both components are likely to be of approximately the same age. We infer that they are both remagnetizations, associated with the deformation. A review of the Paleozoic paleomagnetic data reported by other authors from adjacent areas shows that similar remagnetization situations may prevail. It is concluded that the northeast part of south China has experienced pervasive remagnetizations at the time of folding. The direction of this folding-induced remagnetization yields a new well-defined paleopole position (56-degrees-N, 314-degrees-E) for south China. Although this paleopole is significantly different from Mesozoic poles reported to date, we infer that a Triassic to Jurassic age is most likely for this remagnetization.