酒西盆地晚二叠世古地磁极及其大地构造意义

THE LATE PERMIAN POLE OF THE WESTERN JIUQUAN BASIN (NW CHINA) AND ITS TECTONIC IMPLICATION

本文根据甘肃酒西盆地大黄沟剖面上二叠统“窑沟群”的古地磁资料确定了该盆地晚二叠世古地磁极位置及该区与华北地块的大地构造关系。剖面厚度约684米,共采集33层58个样品。对全部样品进行系统退磁处理后分离出了次生成因的低温分量和原生成因的高温分量。高温分量磁化方向经倾斜改正后密集度显著增强,平均磁化方向为-28.0°N/132.9°E(α95=4.7,K=47.1),相应的古地磁位于42.4°N/350.9°E(A95=3.9,K=67.8),均以99％以上的置信度通过了褶皱检验。由此可知,高温分量是在岩层发生褶皱之前获得的厚生剩磁,所代表的时限属基亚曼反向极性间隔。上述古地磁极位置与其他作者在山西、河北等地获得的结果极为相近,表明酒西盆地至少在晚二叠世就是华北地块的一部分。华北地块与塔里木地块在晚二叠世期间是两个独立的大地构造单元,古边界应位于酒西盆地以西,很可能是阿尔金断裂的前身或与之相当的断裂构造。

A mean direction of-28 °N/132.9° E (α-95 = 4.7, k = 47.1) and a corresponding pole at 42.4 ° N / 350.9 ° E (α-95 = 3.9, K = 67.8) were obtained from 21 out of 33 Upper Permian samples of continental sedimentary rocks collected from the Western Jiuquan Basin, over 1300km west to the places where previous paleomagnetic researches were con- ducted for North China Block. The fair consistency of our results with the preexisting coeval ones demonstrates paleomagnetically that this area was a part of North China Block during Late Permian. If all the preexisting data from both North China and Tarim Blocks are assumed to be precise enough, then the ancient boundary between them should have been west to the Western Jiuquan Basin. The predecessor of Altyn fault or an analoque seems to be the first possible candidate to be chosen as this kind of ancient boundary.