Rapid apparent polar wandering of South China during the latest Paleozoic and early Mesozoic: A paleomagnetic study of Upper Permian limestones from Guizhou province

Abstract

Wang, Z. and Van der Voo, R., 1993. Rapid apparent polar wandering of South China during the latest Paleozoic and early Mesozoic: a paleomagnetic study of Upper Permian limestones from Guizhou province. Tectonophysics, 222: 165–176. The lower part of Upper Permian (~ 265 Ma) marine platform limestones in Guizhou province (South China Block) was sampled for paleomagnetic study. A total of 24 samples from 4 sites was collected. Progressive thermal demagnetization isolated single characteristic component magnetizations from 21 samples. The samples show mixed, but dominantly normal polarities. The mean direction is 46/23 (in-situ) and 53/11 (tilt-corrected), yielding a pole position of 34N, 208E. IRM acquisition experiments suggest that the magnetizations are carried by magnetite. SEM images of polished thin-sections show that the magnetite has replaced pyrite, indicating a secondary (diagenetic) origin for the magnetite. Considering the dominant normal polarity and by comparison with paleomagnetic results of Permian and younger ages for South China, we infer that these Upper Permian limestones in Guizhou province have been remagnetized during the latest Permian or Early Triassic. A review of the paleomagnetic data reported thus far for the Emeishan Basalts in different localities shows that the results from these Upper Permian rocks in general fall into three groups: one group (A) resembles the mean characteristic direction of our limestones; the second group (B) has yielded directions in agreement with those of the Triassic; and the third group (C) conforms to the directions obtained from the Late Triassic/Jurassic remagnetization data in some Paleozoic and Triassic rocks of South China. SEM observations of Emeishan Basalts thin-sections indicate that the A group directions most likely represent the primary magnetizations, while the B group directions are remagnetizations. A late Paleozoic/early Mesozoic apparent polar wander path for South China can thus be constructed by connecting these poles. Paleopoles calculated from northerly folding-associated remagnetizations (C) also fall on this path and are the youngest. This apparent polar wander path points to larger-scale rotations of the South China Block during the late Paleozoic and early Mesozoic than previously thought.