Paleomagnetic Results From Neoproterozoic Madiyi Formation And Middle Devonian Yuntaiguan Formation In South China And Their Tectonic Implications

For reconstructing the connection and separation process between South China and Gondwana during the Paleozoic,and restoring the relative position of South China to other continents in the Neoproterozoic supercontinent Rodinia,systematic paleomagnetic research was conducted on red beds from the Middle Devonian Yuntaiguan Formation(Fm)and Ne-oproterozoic Madiyi Fm in west and northwest Hunan Province,South China,as well as Zircon U-Pb dating on ash beds within the Madiyi Fm.After detailed rock magnetic experiments and stepwise demagnetizations,a well-de-fined characteristic remanent magnetization(ChRM)component carried by hematite was ob-tained from the Yuntaiguan Fm samples.The ChRM passed both fold and reversal tests,and yielded a paleopole of 33.6°N,236.4°E(A95=3°).For the Madiyi Fm,two consistent SIMS zircon 206Pb/238U dates(801.9± 6.3 and 804.6±9.6 Ma)were obtained,and a stable hematite-carrying ChRM passing reversal test was identified,yielding a-800 Ma paleopole of 34.30N,82.4°E(dp=3.7°,dm=3.9°).The two poles differ from all younger pole from the SCB,strengthening the interpretation of their primary origin.The two poles provide critical constraints on South China's position at?800 Ma and Middle Devonian(-385 Ma).The fitting of apparent polar wander paths between South China and Gondwana suggests that South China connected to East Gondwana from the ear-liest Cambrian to Early Devonian(?540-400 Ma),with its southeastern margin closing to northwest Australia.South China broke up from Gondwana during?400-385 Ma,accompa-nied with the opening of the Paleo-Tethys Ocean between them.Thereafter,as East Gond-wana moved towards high latitudes,South China remained in equatorial zone,with the ocean spreading continually.By?360 Ma,South China was separated from East Gondwana by the ocean with a N-S width of?1,600 km.This paleogeographic evolution model based on pale-omagnetic data was supported by the evidence of geologic correlation,provenance analysis and biography.The pole from the Madiyi Fm reveals a high-latitude position of South China at?800 Ma,which is similar to the paleolatitude at?820 Ma.However,coeval poles from the global palaeomagnetic database,along with geological evidence,indicate that East Svalbard,Australia and Laurentia were located around the equator at?800 Ma.The striking difference in paleolatitude suggests that the SCB was unlikely to be located between southeastern Aus-tralia and western Laurentia in the Rodinia supercontinent at?800 Ma.