华北淮北群及新元古代基性岩床构造古地磁学研究

发布时间：2018-05-22 17:31

  本文选题：华北地台 + 新元古代早期　； 参考：《中国地质大学(北京)》2016年博士论文

【摘要】：华北地台中、新元古代地层发育完好,地层连续,构造简单,适于开展古地磁研究,且已取得了很好的结果,为前寒武纪Rodinia和Nuna超大陆恢复提供了重要约束。出露在地台东南缘的淮北群为一套稳定的碎屑海相碳酸盐岩地层,最近的年代学结果表明其为中元古代末-新元古代早期的地层。因而,选择淮北群开展新的古地磁研究,对于确定华北地台在Rodinia超大陆中的位置具有重要意义。对淮北群,包括望山组薄层泥灰岩及侵入其中的~890 Ma辉绿岩墙、贾园组砂质灰岩和泥质粉砂岩、倪园组薄层灰岩与白云质灰岩及侵入其中的~925Ma岩床以及山东苍山地区新兴组红层,共128个采点1001块样品开展了古地磁研究。岩石磁学实验(等温剩磁获得曲线及其反向退磁曲线测量、三轴等温剩磁的系统热退磁分析和磁化率随温度的变化曲线)结果显示各岩石单元携磁矿物分别为:望山组灰岩主要为磁铁矿;侵入其中的~890 Ma辉绿岩床为磁铁矿;贾园组的主要携磁矿物是磁铁矿,~925 Ma辉绿岩床主要为磁铁矿,新兴组为赤铁矿。本次研究的多数样品具有双分量特征。低温分量在0-300℃之间获得,主要为现代场方向;高温分量在450-580℃之间获得。采点平均后,贾园组高温分量为D=186.0°,I=3.8°,a95=6.7°,对应古地磁极为:54.0°S,107.3°E(A95=4.0°)。~925 Ma岩床样品特征剩磁方向的平均方向为:D=162.7°,I=39.7°,a95=3.3°;对应的古地磁极为:30.9°S,136.2°E(A95=3.8°)。望山组的特征剩磁方向为D=337.2°,I=-44.1°,a95=4.8°,可以通过褶皱检验,说明该方向可能为原生剩磁方向,采点平均磁极位置为26.1°N,320.3°E(A95=5.2°)。侵入望山组的~890Ma辉绿岩床样品特征剩磁方向为:D=341.1°,I=1.4°,a95=5.0°;该特征剩磁方向可以通过倒转检验、褶皱检验和烘烤检验,说明该方向为岩床侵入时的原生剩磁方向,古地磁极位置为:52.6°N,330.0°E(A95=5.3°)。本研究显示,在淮北群中下部沉积期间,华北位于赤道附近,望山组形成于中纬度地区,在此之后,华北克拉通向赤道方向移动,~890 Ma时期到达赤道附近。根据本文得到的华北克拉通最新的古地磁数据,从1120-890 Ma,华北克拉通的极移曲线显示一个环形,本文命名其为“淮北环”。根据“淮北环”和“Sveconorwegian环”在年龄和形状上的相似性,华北克拉通和波罗的大陆可能都是Rodinia超大陆的一部分。结合劳伦大陆和波罗的大陆连接的“right-way up”模式及劳伦大陆和西伯利亚大陆之间的关系,华北克拉通可能和劳伦大陆具有较大的亲缘性。
[Abstract]:The Neoproterozoic strata in North China Taizhong are well-developed, continuous, simple in structure, suitable for paleomagnetic research, and good results have been obtained, which provide important constraints for Precambrian Rodinia and Nuna supercontinent restoration. The Huaibei Group, which is exposed in the southern margin of Taitai, is a set of stable clastic marine carbonate strata. Recent geochronological results indicate that the formation is of late Mesoproterozoic to early Neoproterozoic. Therefore, it is of great significance to select a new paleomagnetic study in the Huaibei Group for determining the position of the North China platform in the Rodinia supercontinent. For the Huaibei Group, including the Wangshan formation, the thin layer marl and the intrusive 890 Ma diabase dike, Jiayuan formation sandy limestone and argillaceous siltstone, Paleomagnetic studies were carried out on 1001 samples of thin layer limestone and dolomitic limestone of Ni Yuan formation and the intrusive rock bed of 925 Ma and the new formation of Cangshan area, Shandong Province. Rock magnetic experiment (measurement of isothermal remanence acquisition curve and reverse demagnetization curve, The systematic thermal demagnetization analysis of triaxial isothermal remanence and the variation curve of magnetic susceptibility with temperature show that the magnetic minerals of each rock unit are: the limestone of Wangshan formation is mainly magnetite, and the diabase deposit of 890 Ma intruded into it is magnetite. The main magnetic carrying minerals of Jiayuan formation are magnetite and hematite. Most of the samples in this study have dual component characteristics. The low-temperature component is obtained in the range of 0-300 鈩，

本文编号：1922992