New paleomagnetic results from Late Ordovician rocks of the Yangtze Block, South China, and their paleogeographic implications
New paleomagnetic results from Late Ordovician rocks of the Yangtze Block, South China, and their paleogeographic implications
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华南扬子地块晚奥陶世岩石古地磁新结果及其古地理意义
DOI：
10.1002/2015jb012005
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发表时间：
2015-07-01
影响因子：
3.9
通讯作者：
Jing, Xianqing
中科院分区：
文献类型：
--
作者：
Han, Zhirui;Yang, Zhenyu;Jing, Xianqing
中国南方与澳大利亚在奥陶纪的古地理关系对认识中国南方在冈瓦纳大陆的形态具有重要意义。然而，高质量的奥陶系古地磁结果的扬子地块是稀缺的。本文报道了北方扬子地块旺苍县晚奥陶世灰岩的古地磁研究结果。通过详细的分步热退磁分离出两个磁性成分。低温分量福尔斯落在接近当地电流地球磁场方向。根据磁铁矿所携带的高温分量（HTC），经层理校正后得到的场地平均方向为D/I=132.6度/-35.2度（（95）=3.6度），得出古地磁极位于南纬45.8度，东经191.3度（dp=2.4度，dm=4.2度）。HTC方向经过反转和褶皱检验，其对应的磁极与华南地块志留纪以来的古磁极不同。这些结果表明，在沉积的最早阶段，可能获得的reversium磁化。高温分量的古纬度为19.5 ° S，表明扬子地块在晚奥陶世处于热带纬度。这些新的可靠的古地磁结果填补了奥陶纪的数据空白，有利于中国南方和澳大利亚在晚奥陶纪的接近。
The paleogeographic relationship between South China and Australia during the Ordovician is important for understanding the configuration of South China in Gondwana. However, high-quality Ordovician paleomagnetic results for the Yangtze Block are scarce. Here we report the results of a new paleomagnetic study of the Late Ordovician limestones of Wangcang County in the northern Yangtze Block, performed in order to constrain the paleoposition of South China. Two magnetic components were isolated by detailed stepwise thermal demagnetization. The low-temperature component falls close to the local current Earth's field direction. The site-mean direction obtained from the high-temperature component (HTC) carried by magnetite is D/I=132.6 degrees/-35.2 degrees ((95)=3.6 degrees) after bedding correction, yielding a paleomagnetic pole at 45.8 degrees S, 191.3 degrees E (dp=2.4 degrees, dm=4.2 degrees). The HTC direction passed reversal and fold tests, and its corresponding pole differs from the available paleomagnetic poles since the Silurian of the South China Block. These results suggest that the remanent magnetization was probably acquired during the earliest stage of sedimentation. The high-temperature component yields a paleolatitude of 19.5 degrees S, implying that the Yangtze Block was at tropic latitudes during the Late Ordovician. These new and reliable paleomagnetic results bridge the Ordovician data gap and favor the proximity between South China and Australia during the Late Ordovician.