河西走廊和阿拉善东缘地区中寒武世古地磁研究的初步结果

PRELIMINARY RESULT AND ITS TECTONIC IMPLICATIONS OF MIDDLE CAMBRIAN PALEOMAGNETISM IN THE ALASHAN AND HEXI CORRIDOR TERRANE

用河西走廊和阿拉善地体东缘中寒武世１５个采点１０７块定向岩芯样品，进行岩石 磁学实验和古地磁学研究，结果表明，所采样品以磁铁矿为主要载磁矿物，高温特征分量Ｂ４组 分在９５％置信水平下通过了褶皱检验，其构造校正后的方向明显区别于华北地块及河西走廊 和阿拉善地区志留纪以来的特征剩磁方向．这一组分对应的古地磁极位置（３４９．９°Ｅ，２１．１°Ｎ， ９５％置信圆锥半顶角Ａ_（９５）为１４．９°）与华北地块同时期的极位置相近；表明河西走廊和阿拉善 地体与华北地块主体之间，在中寒武世之后未发生明显的纬向相对运动；但在中寒武世－奥陶 纪期间，河西走廊和阿拉善地体相对于华北地块主体仍可能发生１５°左右的逆时针旋转．这 一旋转作用可能代表了河西走廊和阿拉善地体与华北地块主体的增生过程，最终在晚寒武世 形成统一的华北地块。

This study reports the paleomagnetic results of 107 orientated drill-core Middle Cambrian samples at 15 sites of the east of the Alashan and Hexi Corridor terrane. Detailed paleomagnetic and rock magnetic studies yield that sampled rocks are magnetically predominant of magnetite, and the high temperature component B4 passed fold test at the 95% confidence level. The directions of this component after hit correction are significantly different from post--Silurian ones of the North China Block and the Alashan and Hexi Corridor terrane. The corresponding paleomagnetic pole is at 349.9°E, 21.1°N with A_(95) = 14.9°, which is close to that of the North China Block. This implies that no distinct latitudinal displacement occurred between the Alashan-Hexi Corridor terrane and the North China Block since the Middle Cambrian. Nonetheless, the Alashan and Hexi Corridor terrane may rotate counterclockwise about 15° with respect to the North China Block during the Middle Cambrian through to Late Cambrian. This rotation may indicate that there was an accreting course of the Alashan and Hexi Corridor terrane to the west of the North China Block, and then one united North China Block was formed in the Late Cambrian.