New Late Permian paleomagnetic results from Qaidam block and tectonic implications.
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摘要: 通过对柴达木地块天峻县组合玛地区晚二叠世13个采点的系统古地磁测定,揭示了一组高温特征剩磁分量。实验结果表明,采样剖面获得的晚二叠世古地磁结果具有正、反极性,其特征剩磁方向为:Dg=333.7°, Ig=37.3°, κg=35.4, N=9,α95=8.8; Ds=333.9°, Is=41.7°, κs=69.9, α95=6.2°, 相对应的古地磁极位置为:64.0°N, 342.4°E,A95=5.9°,古纬度为24.0°N。这一高温分量通过了倒转检验,我们认为这一高温特征剩磁分量很可能代表了研究区晚二叠世时期的原生特征剩磁。通过对比塔里木地块晚石炭-晚二叠世古地磁结果,发现两块体在晚石炭世存在明显的古纬度差(16.6±9.3°),而在晚二叠世其古纬度差(3.5±5.4°)在古地磁误差范围内并没有明显差别,从构造意义上说,说明柴达木地块在晚二叠世已是塔里木地块的一部分,结合地质资料,认为柴达木地块在晚二叠世时古地理位置处于塔里木地块的南缘或西南缘,这表明柴达木/塔里木地块间的古阿尔金断裂的形成时代不可能早于晚石炭世时,很可能形成于晚二叠世以后。Abstract: We present paleomagentic results on the Late Permian rocks in the Qaidam block near localities of Zuhema (37.49°N/99.07°E). A total 13 sites have been sampled from Late Permian sediments. Stepwise thermal demagnetizating has revealed a characteristic remanent magnetization (ChRM). Both normal and reversal polarities were observed in studied section, and the high-temperature components pass reversal tests at the 95% confidence level. This indicates the possibly primary magnetization. The tilt-corrected mean directions for the Late Permian is D/I=333.9°/41.7° with a95=6.2° and N=9 sites, corresponding to a paleopole at 64.0°N, 345.4°E, dp/dm=4.7/7.6. Compared with the Late Carboniferous and Late Permian poles from the Tarim block, insignificant post-Late Permian northward motion may have occurred between the Qaidam block and the Tarim block. Also, on the basis of the similarity of rocks of basement and the paleontology for the Qaidam block and Tarim block, the Qaidam block may be a part of the Tarim block, or the two blocks were in close proximity since the Late Permian. This Late Permain paleogeographic reconstruction indicates that the Altyn Tagh fault between the Tarim and Qaidam blocks may begin to form, at least until Late Permian.
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Key words:
- Late Permian /
- Qaidam block /
- Paleomagnetic /
- Paleogeographic reconstruction /
- Altyn Tagh fault
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