An early bird from Gondwana: Paleomagnetism of Lower Permian lavas from northern Qiangtang (Tibet) and the geography of the Paleo-Tethys
An early bird from Gondwana: Paleomagnetism of Lower Permian lavas from northern Qiangtang (Tibet) and the geography of the Paleo-Tethys
复制标题
冈瓦纳大陆的早期鸟类：羌塘北部下二叠统熔岩的古地磁和古特提斯洋的地理
DOI：
10.1016/j.epsl.2017.07.023
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发表时间：
2017
影响因子：
5.3
通讯作者：
Yue Yahui
中科院分区：
文献类型：
--
作者：
Song Peiping;Ding Lin;Li Zhenyu;Lippert Peter C.;Yue Yahui
北羌塘地块的起源及其晚古生代-早中生代的漂移史仍有争议，主要原因是前中生代单元的古地磁约束稀疏且质量差。本文提供了羌塘地块北部下二叠统开心岭群火山岩中一个坚固的、年代确定的古磁极。该极表明羌塘地块北部在约296.9±1.9 Ma的古纬度为21.9±4.7°S。这是首次从羌塘地块前中生代岩石中获得的基于火山的古地磁结果，这些结果似乎足以准确地平均长期变化，从而得出一个确定的古纬度估计。这个新的极点证实了一种假设，这种假设最初是基于不太严格的古地磁数据、双晶岩的存在、碎屑锆石的来源记录和动物组合而提出的，即羌塘北部地块在二叠纪之前从冈瓦纳断裂而出。前人的研究表明，北羌塘地块是在诺里亚时代向塔里木-华北大陆吸积的。我们计算出在约100 myr内向北漂移约7000公里，这相当于南北板块的平均速度约7.0厘米/年。我们的研究结果不支持羌塘北部具有月桂系亲缘关系的结论，也不支持羌塘中部变质带为古特提斯系原位缝合的结论。然而，我们的分析并不排除将中央羌塘变质带解释为在冈瓦南边缘以外的南纬地区发育的羌塘内缝合线的古地理。我们强调，来自北羌塘石炭系单元，特别是南羌塘上古生界单元的严格古地磁资料可以检验和进一步完善这些古地理解释。
The origin of the northern Qiangtang block and its Late Paleozoic–Early Mesozoic drift history remain controversial, largely because paleomagnetic constraints from pre-Mesozoic units are sparse and of poor quality. In this paper, we provide a robust and well-dated paleomagnetic pole from the Lower Permian Kaixinling Group lavas on the northern Qiangtang block. This pole suggests that the northern Qiangtang block had a paleolatitude of 21.9±4.7° S at ca. 296.9±1.9 Ma. These are the first volcanic-based paleomagnetic results from pre-Mesozoic rocks of the Qiangtang block that appear to average secular variation accurately enough to yield a well-determined paleolatitude estimate. This new pole corroborates the hypothesis, first noted on the basis of less rigorous paleomagnetic data, the presence of diamictites, detrital zircon provenance records, and faunal assemblages, that the northern Qiangtang block rifted away from Gondwana prior to the Permian. Previous studies have documented that the northern Qiangtang block accreted to the Tarim-North China continent by Norian time. We calculate a total northward drift of ca. 7000 km over ca. 100 myr, which corresponds to an average south-north plate velocities of∼ 7.0 cm/yr. Our results do not support the conclusion that northern Qiangtang has a Laurasian affinity, nor that the central Qiangtang metamorphic belt is an in situ Paleo-Tethys suture. Our analysis, however, does not preclude paleogeographies that interpret the central Qiangtang metamorphic belt as an intra-Qiangtang suture that developed at southernly latitudes outboard of the Gondwanan margin. We emphasize that rigorous paleomagnetic data from Carboniferous units of northern Qiangtang and especially upper Paleozoic units from southern Qiangtang can test and further refine these paleogeographic interpretations.