Paleomagnetism and U‐Pb zircon geochronology of Lower Cretaceous lava flows from the western Lhasa terrane: New constraints on the India‐Asia collision process and intracontinental deformation within Asia
Paleomagnetism and U‐Pb zircon geochronology of Lower Cretaceous lava flows from the western Lhasa terrane: New constraints on the India‐Asia collision process and intracontinental deformation within Asia
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DOI：
10.1002/2014jb011362
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发表时间：
2014-10
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通讯作者：
Yiming Ma;Tianshui Yang;Zhenyu Yang;Shihong Zhang;Huaichun Wu;Haiyan Li;Huai-kun Li;Weiwei Chen-
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作者：
Yiming Ma;Tianshui Yang;Zhenyu Yang;Shihong Zhang;Huaichun Wu;Haiyan Li;Huai-kun Li;Weiwei Chen-
为了更好地了解印度-亚洲碰撞过程和亚洲内部的陆内变形，对拉萨地体西部盐湖地区~132~120 Ma的库什拉组熔岩流进行了古地磁研究。阶梯式热退磁隔离稳定的特征剩余磁化，包括双极性，并在99%的置信度下通过折叠测试，表明初级磁化。经倾斜校正的51个测点的平均方位为D=2 8.2°，I=34.5°，k=74.3°，α95=2.3°，对应于北纬61.4°，东经192.9°(A95=2.1°)的古极点。我们新的古地磁资料结合以前的拉萨地体白垩纪火山古地磁资料表明，亚洲碰撞前南缘位于~16.8°N，相对东西走向，拉萨地体没有经历明显的南北运动，尽管在白垩纪之后发生了局部的垂直轴旋转。与印度和特提斯喜马拉雅白垩纪-古新世古极地的视极移路径(APWPs)对比表明，印度-亚洲碰撞的年龄约为54.3 Ma，古新世大印度的北部范围比现在的北缘高出约2000公里(约18.1°)。与白垩纪欧亚APWP的对比表明，自印度-亚洲碰撞以来，拉萨地体与欧亚大陆之间发生了约1000公里的纬向会聚。根据白垩纪古地磁资料推断的南北缩短幅度与拉萨地体与河西走廊之间的新生代褶皱冲断带所容纳的南北缩短幅度一致。
To better understand the India‐Asia collisional process and intracontinental deformation within Asia, a paleomagnetic study has been conducted on the Qushenla Formation lava flows dated at ~132–120 Ma from the Yanhu area in the western Lhasa terrane. Stepwise thermal demagnetization isolates stable characteristic remanent magnetizations, which include dual polarity and pass fold tests at a 99% confidence level, indicating primary magnetizations. The tilt‐corrected site‐mean direction for 51 sites is D = 28.2°, I = 34.5°, and k = 74.3° with α95 = 2.3°, corresponding to a paleopole at 61.4°N, 192.9°E (A95 = 2.1°). Our new paleomagnetic data, combined with previous Cretaceous volcanic paleomagnetic data from the Lhasa terrane, show that the precollisional southern margin of Asia was at ~16.8°N with a relatively E‐W alignment and that the Lhasa terrane did not experience significantly discrepant north‐south movement although local vertical axis rotations did take place after the Cretaceous. Comparison with the apparent polar wander paths (APWPs) of India and the Cretaceous‐Paleocene paleopoles of the Tethyan Himalaya shows that the India‐Asia collision was at ~54.3 Ma and the Greater India during the Paleocene had a large northern extent of ~2000 km (~18.1°) beyond its present northern margin. Comparison with the Cretaceous Eurasian APWP indicates that a latitudinal convergence of ~1000 km has taken place between the Lhasa terrane and Eurasia since the India‐Asia collision. The amount of north‐south shortening deduced from Cretaceous paleomagnetic data is consistent with that accommodated by the Cenozoic fold and thrust belts between the Lhasa terrane and the Hexi corridor.