Paloemagnetism Of Mesoproterozoic Mafic Dyke Swarms In The North China Craton, And Its Tectonic Implication

As an essential feature of global tectonic evolution, the convergence andbreaking up of supercontinent fundamentally control the evolution and developmentof all the continents on the earth. The intact reconstruction model of Columbiasupercontinue is lack in sufficient reliable paleomagnetic data. The midproterozoicpaleomagnetic poles from the North China Craton are not sufficient and came fromsedimentary units, short of chronological restraint, so that they can’t explaingeotectonic determinately. A mass of mafic dyke swarms spreaded in themidproterozoic sedimentary strata of the North China Craton. Recently, somegeologists have made chronological advances on these mafic dyke swarms.Consequently, we do systematic paleomagnetic research on the mafic dyke swarmsemplaced in the midproterozoic sedimentary strata of the North China Craton.Totally385paleomagnetic cores were collected from34sites seated in HuailaiCounty, Kuancheng County of Hebei Province and Jixian County of Tianjin. Wecarried out paleomagnetic and rock magnetic studies on these samples. The rusultsfrom rock magnetic experiments consisting of acquisition of isothermal remanentmagnetization （IRM） and k-T curve indicated that the main magnetic mineral wasmagnetite. Analysis and results of stepwise thermal demagnetization showed greatmajority samples had two components, with the low temperature componentremagnetized by the modern geomagnetic field. Recenntly，mafic dyke swarms inKuancheng County were precisely dated at1325±5Ma by U-Pb dating method. It’sworth noting that the high component B isolated from Xinjiazhuang profile inKuancheng County has double polarity and symmetrical character, with site-meandirections for10sites D=119.2°，I=27.0°，k=149.0，α₉₅=4.2°N=9，in geographiccoordinates and D=86.3°，I=32.7°，k=116.1，α₉₅=4.8°，N=9， in stratigraphiccoordinates respectively, corresponding to a paleopole at14.2°N，196.7°E，α₉₅=4.8°，dp/dm=3.1°/5.4°, and paleolatitude17.8°N.The position of the midproteromic paleomagnetic pole from this study draw nearto the position of other paleomagnetic poles from the mesoproterozic sedimentarybeds in the North China Craton, indicating the North China Craton was seated in themid-low latitudes during the midproterozoic period. Comparing this paleomagneticpole with the Apparent Polar Wander Path or paleomangnetic pole of other relatedcontinents during1820Ma to1265Ma, we propose that the North China Craton was connected with Siberia continent, Baltica continent and Laurentia continentconsistently, drifting together from1820Ma to1320Ma.