New Cretaceous paleomagnetic poles from the Tarim Basin, Northwestern China
New Cretaceous paleomagnetic poles from the Tarim Basin, Northwestern China
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DOI：
10.1016/0012-821x(92)90149-p
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发表时间：
1992-12
影响因子：
5.3
通讯作者：
Yan Chen;J. Cogné;V. Courtillot
中科院分区：
文献类型：
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作者：
Yan Chen;J. Cogné;V. Courtillot
塔里木盆地的古地磁研究主要集中在古生代，中生代的古地磁资料很少。然而，亚洲这一部分的古代构造受到了印度-欧亚碰撞的影响。在1990年秋季从喀什卡尔到Kunjerab的第二次法中喀喇昆仑考察期间，我们从乌依塔克、英吉沙和乌恰附近的三个地区（38.5-39.5°N，75-76.5°E）的53个上白垩统和下白垩统红砂岩地点采集了约500个岩心。等温剩磁采集表明存在高磁化率矿物。逐步热退磁证实了赤铁矿是主要载体，并且允许在大多数样品中低温组分（LTC，< 300°C）与高温组分（HTC，> 600°C）分离。LTC的平均方向与当前地球场的方向一致。正常和反向极性已被发现为每个年龄组的HTC。HTC显示至少一项子研究的阳性折叠试验，其中垫料的姿态差异足以进行试验。更重要的是，英吉沙和乌恰的四个子研究给出了完全一致的结果。从Uytak地区的结果表明，广泛的分散在磁偏角，可以预期从相当严重的变形和接近主要的逆冲断层和走滑断层。在塔里木北方库车地区由李和同事获得的数据和在准噶尔南部由陈和同事获得的数据在统计学上与在英吉沙和乌恰获得的新数据一致。来自塔里木北方派城的数据似乎受到局部旋转的影响。排除古地磁研究中出现明显旋转的地点，计算出塔里木盆地白垩纪的平均极位为69.1°N°，223.8°E（A95= 3.5°，N= 5）。这一结果表明，塔里木盆地相对于准噶尔盆地和欧亚大陆的后白垩纪总自转量（分别为2.6 ± 6.1°和0.4 ± 4.6°）可以忽略不计。天山地区塔里木-准噶尔之间的大陆缩短和旋转，虽然所获得的值（400 ± 600 km，3 ± 6°）与该地区的构造模型相一致，但不能用古地磁学来解释。在进一步的地质调查中，一个主要的差异是塔里木和华北块体两极之间的差异，这意味着南北相对位移约为1400 ± 1060 km。
Most paleomagnetic studies of the Tarim have been focused on the Paleozoic, with little data published for Mesozoic rocks. However, the ancient configuration of this part of Asia has been affected by the Indian-Eurasian collision. During the second French-Chinese Karakorum expedition, from Kashkar to Kunjerab, in the Autumn of 1990, we sampled about 500 cores from 53 sites of Upper and Lower Cretaceous red sandstones from three areas near Uytak, Yingjisha and Wuqia (38.5–39.5°N, 75–76.5°E). Isothermal remanent magnetization acquisition indicates the presence of minerals with high magnetic coercivity. Stepwise thermal demagnetization confirms that hematite is the dominant carrier and allowed the separation of low temperature components (LTC, < 300°C) from high temperature components (HTC, > 600°C) in most samples. The mean direction of LTCs is aligned with that of the present Earth field. Normal and reversed polarities have been found for the HTCs of each age group. HTCs show positive fold tests for at least one sub-study where the attitudes of bedding were sufficiently different to allow the test to be performed. More important, the four sub-studies from Yingjisha and Wuqia give fully compatible results. Results from the Uytak area show a wide dispersion in declinations, as could be expected from the rather severe deformation and proximity to major thrust and strike-slip faults. Data obtained in the Kuche area from northern Tarim by Li and co-workers and in southern Junggar by Chen and co-workers are statistically identical to the new data from Yingjisha and Wuqia. Data from Paicheng in northern Tarim appear to have been subject to local rotation. Excluding those sites which appear from paleomagnetic study to have been significantly rotated, we calculated a mean Cretaceous pole for the Tarim basin at 69.1°N°, 223.8°E (A95= 3.5°,N= 5). This result indicates that the total post-Cretaceous rotation of Tarim relative to Junggar and to Eurasia has been negligible (2.6 ± 6.1° and 0.4 ± 4.6°, respectively). Continental shortening and rotation between Tarim and Junggar, within the Tien Shan, are not resolved by paleomagnetism although the values obtained (400 ± 600 km, 3 ± 6°) are compatible with tectonic models of the range. A major discrepancy, warranting further geological investigation, is that between the Tarim and North China block poles, which would imply some 1400 ± 1060 km of north-south relative displacement.