Resolving the problem of shallow magnetizations of Tertiary age in Asia: insights from paleomagnetic data from the Qiangtang, Kunlun, and Qaidam blocks (Tibet, China), and a new hypothesis
Resolving the problem of shallow magnetizations of Tertiary age in Asia: insights from paleomagnetic data from the Qiangtang, Kunlun, and Qaidam blocks (Tibet, China), and a new hypothesis
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DOI：
10.1029/1999jb900153
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发表时间：
1999-08
影响因子：
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通讯作者：
J. Cogné;Nadir Halim;Yan Chen;V. Courtillot
中科院分区：
文献类型：
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作者：
J. Cogné;Nadir Halim;Yan Chen;V. Courtillot
本文介绍了西藏羌塘地块第三纪红层建造五个剖面39个采样点的古地磁新结果（下拉秀地区; 32.8°N，96.6°E）和柴达木西宁盆地（西宁地区; 36.5°N，102.0°E）和西宁盆地新近系三个建造昆仑地块（托洛湖和玉树西部地区，分别为35.3 °N，98.6°E和33.2°N，96.7°E）。热退磁的岩石孤立的高温成分，我们解释为主要磁化在四个地方。下拉秀古极点位于52.6°N/352°E（dp/dm = 6.0°/10.7°），西宁古极点位于61.6°N/211.3°E（dp/dm = 9.7°/16.1°），军贡古极点位于66.0°N/228.6°E（dp/dm = 3.6°/6.9°），玉树西部古极点位于53.9°N/205.4°E（dp/dm = 5.6°/10.0°）。与以前对亚洲第三纪地层的研究一样，我们获得的倾角比根据欧亚表观极移路径（APWP）计算的磁场要浅（18°至26°），其中新近纪岩石在10和20 Ma，始新世岩石在40和60 Ma。根据华南地块、西藏、中亚和吉尔吉斯斯坦始新世的资料，我们认为这种倾斜异常反映了根据欧亚大陆的APWP对西伯利亚克拉通位置的错误预测。这种差异的主要原因可能是第三纪欧亚板块的非刚性行为。这一点与印度渗透下的亚洲陆内缩短相结合，为这一异常现象提供了充分的解释。要验证这种对“倾斜异常”的新解释，需要从蒙古和西伯利亚这些偏远地区的北方获得新的地质和古地磁数据。
We present new paleomagnetic results obtained at 39 sampling sites from five sections of Tertiary red bed formations: two Eocene formations from the Qiangtang block of Tibet (Xialaxiu locality; 32.8°N, 96.6°E) and the Xining basin of Qaidam (Xining locality; 36.5°N, 102.0°E) and three Neogene formations from the Xining basin (Jungong locality; 34.7°N, 100.7°E) and the Kunlun block (Tuoluo lake and West Yushu localities; 35.3°N, 98.6°E and 33.2°N, 96.7°E, respectively). Thermal demagnetization of the rocks isolated a high-temperature component that we interpret as the primary magnetization in four localities. The paleopoles lie at 52.6°N/352°E (dp/dm = 6.0°/10.7°) for Xialaxiu, 61.6°N/211.3°E (dp/dm = 9.7°/16.1°) for Xining, 66.0°N/228.6°E (dp/dm = 3.6°/6.9°) for Jungong, and 53.9°N/205.4°E (dp/dm = 5.6°/10.0°) for West Yushu. As in previous studies of Tertiary formations from Asia, the inclinations we obtained are shallower (by 18° to 26°) than the magnetic field computed from the Eurasian apparent polar wander path (APWP) at 10 and 20 Ma for Neogene rocks and at 40 and 60 Ma for Eocene rocks. On the basis of a compilation of Eocene data from the South China Block, Tibet, central Asia and Kyrgyzstan, we conclude that this inclination anomaly reflects erroneous predictions of positions of the Siberian craton when based on the APWP of Eurasia. The main reason for this discrepancy might be nonrigid behavior of the Eurasian plate in the Tertiary. Combination of this with intracontinental shortening of Asia under the penetration of India provides a full explanation for the anomaly. Verification of this new interpretation of the “inclination anomaly” will require new geologic and paleomagnetic data from the northern parts of these remote regions in Mongolia and Siberia.