【作者】 吴怀春；

【导师】 张世红；

【作者基本信息】 中国地质大学（北京） ， 构造地质学， 2005， 博士

【摘要】 对华北地台蓟县、兴隆和宽城地区的中元古界及中生代髫髻山组共142 个采点,1155 块样品开展了详细的古地磁研究,共分离出13 个方向各异的剩磁分量。在各岩石单元普遍存在的低温分量方向在地理坐标系下与现代地磁场方向接近,是现代场重磁化的结果。9 个高温分量受到后期重磁化或构造扰动的影响。对各岩石单元代表性样品进行了岩石磁学实验(饱和等温剩磁和剩磁矫顽力的测量、三轴等温剩磁的系统热退磁分析和磁化率随温度变化曲线),结果表明多数样品的磁性矿物主要为赤铁矿,或赤铁矿与磁铁矿共存,少数样品的磁性矿物主要为磁铁矿,或以磁铁矿为主,含少量的赤铁矿、针铁矿和磁黄铁矿。从构造稳定的蓟县剖面的杨庄组、雾迷山组和铁岭组获得了最可能的原生剩磁。从杨庄组15 个采点获得的高温剩磁分量在99%置信水平上通过了褶皱检验,在95%置信水平上通过了倒转检验,对应的视磁极位置为17.3°N, 214.5°E(dp=4.1°, dm=8.0°)。从雾迷山组红层中获得的古地磁结果虽然没有野外检验,但很可能代表了原生剩磁方向,视磁极位置为20.2°N, 221.4°E(dp=2.8°, dm=5.5°)。从铁岭组11 个采点获得的高温剩磁分量,在99%置信水平上通过褶皱检验,对应的视磁极位置为11.6°N, 187.1°E(dp=4.9°, dm=8.1°)。对杨庄组、雾迷山组和铁岭组古地磁极的最佳年龄估计值分别为1350,1300 和1120Ma。在全面回顾华北地台古地磁结果的基础上,建立了华北地台中新元古代视极移曲线。根据视极移曲线恢复的古地理位置表明,中新元古代华北地台位于中低纬度地区。通过对华北地台、Laurentia、Baltica 和Siberia 大陆中元古代视极移曲线(或古地磁极)的拟合,并结合前人的研究成果,结果表明在中新元古代期间,这些大陆的相对位置没有发生明显的变化,其中华北地台通过Siberia 与Laurentia 相连,Baltica 与格陵兰相连。1350-1200Ma 期间,华北相对Laurentia发生了大约90o的逆时针旋转。在1265-1070Ma 期间,Baltica 相对格陵兰向南移动了约1500 km, Siberia 则没有发生明显的变化。在1350-1100Ma 期间各大陆连接方式的转换与Columbia 超级大陆的裂解和Rodinia 超级大陆的形成时间对应。兴隆和宽城髫髻山组的高温分量具有稳定的退磁特征,携磁矿物主要为赤铁矿。古地磁结果显示,这两个地区自晚侏罗世以来相对华北稳定地区分别发生了旋转量为115.2°±15.1°和146.1°±13.9°的顺时针旋转,但没有明显的纬向位移。该地区发生的顺时针旋转作用可能与中生代大型右行走滑系统相关。更多还原

【Abstract】 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更多还原