【作者】 张均红；

【导师】 张世红；

【作者基本信息】 中国地质大学(北京) ， 构造地质学， 2012， 硕士

【摘要】 超大陆的聚合与裂解作为全球构造演化的最基本特征，从根本上控制了全球各大陆的构造演化和发展。Columbia完整的古大陆重建方案，目前仍然缺乏足够数量的可靠的古地磁数据。华北克拉通中元古代的古地磁极不仅数量有限，而且大多数来自于沉积地层，缺乏年代学约束，其构造解释仍然含有很大的不确定性。华北克拉通中元古代沉积岩中广泛分布有大量基性岩墙，近年来对这些基性岩墙获得了较好的年代学证据，基于这一进展，本文对华北克拉通中元古代基性岩墙进行系统的古地磁研究。在河北怀来、天津蓟县和河北宽城三个采区34个采点共采集古地磁岩心385块。样品的磁化率随温度变化曲线、等温剩磁获得等岩石磁学实验结果表明，岩墙的主要磁性矿物为磁铁矿。对退磁结果进行分离和分析，结果表明大部分样品具有双分量特征，低温分量多为现代场重磁化结果或粘滞剩磁，高温分量方向集中。目前，对宽城辛家庄研究区的岩墙获得了精确的U-Pb年龄为1325±5Ma，该剖面3条岩墙、10个采点（A10KC07-A10KC16）的高温分量B具有双极性，并表现出很好的对蹠关系，其平均方向在产状校正前和校正后分别为D=119.2°，I=27.0°，k=149.0，α₉₅=4.2°，N=9和D=86.3°，I=32.7°，k=116.1，α₉₅=4.8°，N=9。这一结果在95%置信水平下通过了McFadden&Lowes（1981）的B级倒转检验，表明样品中的高温分量方向很可能是原生剩磁方向，该基性岩墙很有可能记录了岩墙侵位时的古地磁场方向，其对应的极位置为14.2°N，196.7°E，α₉₅=4.8°，dp/dm=3.1°/5.4°，古纬度为17.8°。这一中元古代中期古地磁极KC的位置与前人在华北克拉通相邻时代地层中获得的古地磁极位置比较接近，说明华北克拉通在中元古代的1.35¹.32Ga期间一直位于中低纬度地带。将该磁极与1820¹265Ma期间各大陆视极移曲线或古地磁极进行对比分析，表明在1800¹320Ma期间，华北克拉通与Siberia、Baltica和Laurentia大陆很可能稳定的连接在一起，并保持一致的运动行迹。更多还原

【Abstract】 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.更多还原