New paleomagnetic results for Ordovician and Silurian rocks of the Tarim Block, Northwest China and their paleogeographic implications
New paleomagnetic results for Ordovician and Silurian rocks of the Tarim Block, Northwest China and their paleogeographic implications
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DOI：
10.1016/j.tecto.2019.02.010
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发表时间：
2019-03-20
期刊：
影响因子：
2.9
通讯作者：
Zhao, Qian
中科院分区：
文献类型：
--
作者：
Huang, Baochun;Piper, John D. A.;Zhao, Qian
在晚古生代之前，人们对塔里木地块的运动学知之甚少，本研究旨在澄清奥陶纪和志留纪时期的运动。我们报告了塔里木西北部阿克苏和柯坪地区奥陶纪海相沉积物中的12个站点和志留系细粒砂岩和泥岩中的21个站点的古地磁记录。结合我们之前报道的初步结果，奥陶纪沉积物分离出零星保存的具有双极性的前新生代特征剩磁。尽管正折叠测试只能将剩磁定义为新生代前，但从塔里木志留纪后古极点中删除了相应的古磁极（南纬33.7度，东经185.0度，dp/dm = 2.7度/4.0度），并与磁性织物的证据相结合，表明准原始起源。在阿克苏和卡尔平地区志留纪沉积物的 17 个地点分离出特征性剩磁，其中 7 个地点疑似受到区域二叠纪火成岩活动的污染。其余 10 个地点均来自卡尔平，产生了阳性折叠测试，并且在北纬 19.1 度、东经 172.9 度（A(95) = 5.5 度）处有一个古极点，与来自塔里木的较年轻的古极点显着移除，表明兰多弗里晚期到文洛克剩磁年龄。新的中晚奥陶世古极点将塔里木地块置于南纬32度左右，可能位于冈瓦纳阿拉伯边缘附近。大约460 Ma和大约433 Ma之间的快速APW记录了塔里木和古亚洲洋边缘的其他大陆块的大差异右旋运动，这使得中国大陆块在志留世中期在北纬低纬度（大约北纬9度）靠近澳大利亚。
The kinematics of the Tarim Block is poorly understood prior to the late Paleozoic and this study aims to clarify motions during Ordovician and Silurian times. We report the paleomagnetic record from 12 sites in Ordovician marine sediments and 21 sites in Silurian fine-grained sandstones and mudstones from the Aksu and Kalpin areas of northwestern Tarim. Together with our previously reported preliminary results, the Ordovician sediments isolate a sporadically-preserved pre-Cenozoic characteristic remanence with dual polarity. Although a positive fold test can only define the remanence as pre-Cenozoic, the corresponding paleomagnetic pole (33.7 degrees S, 185.0 degrees E, dp/dm = 2.7 degrees/4.0 degrees) is removed from post-Silurian paleopoles from Tarim and combined with evidence from magnetic fabrics indicating a quasi-primary origin. A characteristic remanence isolated at 17 sites in Silurian sediments from the Aksu and Kalpin areas includes 7 sites with suspected contamination from regional Permian igneous activity. The 10 remaining sites, all from Kalpin, yield a positive fold test and a paleopole at 19.1 degrees N, 172.9 degrees E (A(95) = 5.5 degrees) significantly removed from younger paleopoles from Tarim indicating a Late Llandovery to Wenlock remanence age. The new Mid-Late Ordovician paleopole places the Tarim Block at similar to 32 degrees S, probably in the vicinity of the Arabian margin of Gondwana. Rapid APW between similar to 460 and similar to 433 Ma records large differential dextral motions of Tarim together with other continental blocks along the Paleo-Asian Ocean margin which brought the China continental blocks into proximity with Australia by mid-Silurian times in low (similar to 9 degrees N) northerly paleolatitudes.