New Paleomagnetic Results From Mesoproterozoic Successions In Jixian Area, North China Block, And Their Implications For Paleocontinental Reconstructions

A total of 142 sties, 1155 paleomagnetic samples were collected from the Mesoproterozoic successions and Late Jurassic Tiaojishan Formation in Jixian, Xinglong and Kuancheng areas, North China Block (NCB). Detailed stepwise thermal demagnetizations allowed us to isolate 13 different components. A low temperature component, which exists in all rock units, is interpreted as a remagnetization of recent geomagnetic field. Nine high temperature components may be affected by the remagnetization or local rotation, and their paleogeographic implications are not further discussed in this thesis. Results of rock magnetic study, including IRM acquisitions, three-component IRM thermal demagnetization and temperature dependence of magnetic susceptibility analysis, for representative samples from each rock unit indicated that the predominant magnetic minerals in most samples are hematite or hematite with minor magnetite, and in a few samples are magnetite, or magnetite coexisting with hematite, goethite and pyrrhotite. Three interpreted primary components were derived from the Yangzhuang, Wumishan and Tieling Fromations in Jixian area. The high temperature component isolated from 15 sites of the Yangzhuang Formation can pass fold test at 99% confidence level and reversal test at 95% confidence level. Its corresponding pole locates at 11.6°N, 187.1°E (dp=4.9°, dm=8.1°). The hard component derived from Wumishan Formation has no field test, but may be primary according to its stable high-temperature demagnetization characteristics, and this result is consistent with paleogeographic and paleoclimate proxies resided in rocks. The corresponding paleomagnetic pole locates at 20.2°N, 221.4°E (dp=2.8°, dm=5.5°). Eleven sites of Tieling Formation yields a hard component which can pass fold test at 99% confidence level, and its corresponding pole locates at 11.6°N, 187.1°E (dp=4.9°, dm=8.1°). The best estimated ages for paleomagnetic poles from the Yangzhuang, Wumishan and Tieling Formation are 1350, 1300 and 1120 Ma, respectively. Based on our new results and a critical selection of available data from North China, a new apparent polar wander path (APWP) is compiled for NCB in Meso-to Neoproterozoic. Notwithstanding the alternative polarities applicable to these poles, the NCB was within mid to low latitude zone for much of this time span. After...