Palaeomagnetism of Neoproterozoic glacial rocks of the Huabei Shield: the North China Block in Gondwana : Piper J.D.A. & Zhang Qi Rui, Tectonophysics, 1997, 283/1–4 (145–171)

Abstract

We collected 917 oriented drill-core samples (124 sites) from 22 units spanning the Early Cambrian to Middle Ordovician formations of the North China Block (NCB) to construct an apparent polar wander path (APWP) of the early Paleozoic for the NCB. Sampling areas are located in the Helanshan, Tongchuan-Hancheng and Yuncheng-Luliang regions along the margin of the Ordos Basin. Characteristic remanent magnetizations for five periods between the Cambrian and Ordovician are isolated from 281 samples by careful demagnetization. Directions cluster around northwesterly direction with upward shallow inclination and its antipode after tilt correction. Reliability of these five directions is ascertained through positive fold and reversal tests. The five Cambrian and Ordovician paleopoles plot in the present Atlantic Ocean, which is consistent with previously reported paleomagnetic poles. A newly constructed APWP between the Cambrian and Ordovician indicates that the NCB was located in the Southern Hemisphere around 15°S during Cambro–Ordovician time. Motion of the NCB between the Early and Middle Cambrian comprised: a counterclockwise rotation of 22.3° ± 7.0° and a northward latitudinal displacement of 7.2° ± 6.8°. Combining the paleobiogeographic and paleoclimatic data with the paleomagnetic implies that the NCB was probably located in East Gondwana in the Early Cambrian, and may have separated from Gondwana in post-Early Cambrian time. The NCB is also inferred to have been located close to Siberia and North America during the Middle Ordovician.