Paleomagnetism Of Neoproterozoic Madiyi Formation In The South China Block And Its Tectonics Implications

Neoproterozoic paleomagnetismof South China Block(SCB)is of great significance for supercontinent evolution,Snowball Earth and True Polar Wander hypothesis.Madiyi Formation of Banxi Group,composed of predominantlypurple argillaceous siltstone,isan idealtarget for paleomagnetismbecause of well outcrop,mild deformation andmetamorphose.Paleomagnetic samplesincluding 200 coresof 13 sites,were collected from Guzhangsectioninwest Hunan Province,where theageofMadiyi Fmwas constrained between 814 Maand 809 Ma.All thesamples were subjected to systematic thermal demagnetization and representative samples were performed to rock magnetic experience such as Isothermal Remanent.Thermal demagnetization revealed two components among most samples,thelow temperature component(LTC)and high temperature component(LTC).TheLTC,the direction of which is close to late Jurassic one,is regarded as Mesozoic overprint of SCB.The HTCyielded a mean direction of D=310.0°,I=57.4°,?95=2.7(108samples of 13 sites)and past fold test and reversal test.Considering pervasive inclination shallowing of sedimentary rocks,E/Itechnique was performed to the HTC,with inclination shift to 75.1°,corresponding to a paleolatitude of 62°.The paleopole calculated from inclination-corrected direction is 44.9°N,79.3°E,A95=4.5°,with no similarity with any younger poles of SCB.Besides,the HTCrecords at least threegeomagnetic reversals,indicating frequent reversal around ca.810 Ma.Paleomagnetic results show that SCBmoved from high-latitude(even polar)regionto equator region between ca.825 MaandCambrian.Moreover,when SCBwas at high latitude(825-780 Ma),itwitnessed greenhouse climate(widespread red bed),this combined with coeval sedimentary character at Laurentia and Australia(widespread evaporate),could be anindicator of global warming.Nevertheless,when SCBwas at mid-low latitude(Cryogenian),itwitnessed cold climate(glacial deposits),indicating the response of Snowball Earth in SCB.SCBis the unique continent yet discovered to indicate global climate variation and supported by paleomagnetic and sedimentary evidence.Synthesizing paleomagnetic and geologic evidence,a new model of Rodiniawas reconstructed.In this model,SCBwas located at the northern peripheryof Rodinia,with itwest margin facing north India;Indiawas to the northwest of Australia;northeast Australia connected with southwest Laurentia,like AUSMEX model;Tarim acted as an alternative “Missing-link”,was adjacent to west Laurentia.In the reconstruction mentioned above,the paleopoles at ~820-780 Maof SCB,Svalbard,Australia,Indiaand Laurentiadistributed along a great circle,perhaps representing the True Polar Wander eventaround 800 Ma.