New Early Cretaceous paleomagnetic results from Qilian orogenic belt and its tectonic implications
New Early Cretaceous paleomagnetic results from Qilian orogenic belt and its tectonic implications
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DOI：
10.1360/02yd9059
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发表时间：
2002-06
期刊：
影响因子：
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通讯作者：
Tianshui Yang;Zhenyu Yang;Zhiming Sun;A. Lin
中科院分区：
文献类型：
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作者：
Tianshui Yang;Zhenyu Yang;Zhiming Sun;A. Lin
对东祁连褶皱带沉积盆地下白垩统红色沉积岩进行了古地磁研究。分步热退磁揭示了暗红色砂岩的两个或三个磁化分量。低温磁分量与现今地球磁场在地理坐标上的方向一致。高温磁性组分主要由赤铁矿携带。倾斜校正后的19个高温磁性元件测点的平均极点为λ=62.2° N，θ =193.4° E，A95=3.2°，通过了99%置信水平的折叠检验和95%置信水平的反转检验。在95%的置信水平下，同一采样区的古极点与Halim等人（1998）的古极点差异不显著。与华北、华南和欧亚大陆的古地磁结果相比，我们的结果表明，自白垩纪以来，兰州地区与这些地块之间没有发生明显的相对纬向位移。值得注意的是，兰州的极点相对于华北、华南和欧亚大陆的极点有20°的顺时针旋转。地质资料表明，祁连山西部地壳缩短幅度大于东部。在这种情况下，采样区的顺时针旋转与印度/欧亚大陆碰撞有关，这种碰撞导致了白垩纪后青藏高原北部阿尔金断裂的左行走滑运动。
Lower Cretaceous red sedimentary rocks from the depositional basin of East Qilian fold belt have been collected for a paleomagnetic study. Stepwise thermal demagnetization reveals two or three components of magnetization from dark red sandstones. Low-temperature magnetic component is consistent with the present Earth Field direction in geographic coordinates. High-temperature magnetic components are mainly carried by hematite. The mean pole of 19 sites for high-temperature magnetic components after tilt-correction is λ=62.2° N, ϕ=193.4° E, A95=3.2°, and it passes fold tests at 99% confidence level and reversal tests at 95% confidence level. The paleopole is insignificantly different from that of Halim et al. (1998) from the same sampling area at the 95% confidence level. Compared with paleomagnetic results for North China, South China, and Eurasia, our results suggest that no significant relative latitudinal displacement has taken place between Lanzhou region and these blocks since Cretaceous time. Remarkably, the pole of Lanzhou shows a 20° clockwise rotation with respect to those of North China, South China, and Eurasia. Geological information indicates that the crustal shortening in the western part of Qilian is greater than that in eastern part. In this case, the clockwise rotation of sampling area was related to India/Eurasia collision, and this collision resulted in a left-lateral strike-slip motion of the Altun fault in north Tibetan Plateau after the Cretaceous.