青藏高原羌塘盆地晚三叠世古地磁数据及其构造意义  

Late Triassic Paleomagnetic Data from the Qiangtang Terrane of Tibetan Plateau and Their Tectonic Significances

作　　者：宋春彦[1,2] 王剑[2] 付修根[2] 冯兴雷[2] 陈明[2] 何利[2] 

机构地区：[1]中国地质科学院研究生部,北京100037 [2]成都地质矿产研究所,成都610081

出　　处：《吉林大学学报（地球科学版）》2012年第2期526-535,共10页Journal of Jilin University：Earth Science Edition

基　　金：国家自然科学基金项目(40972087);国家油气专项(选区[2009]01)

摘　　要：羌塘盆地作为青藏高原主要的地体之一,其中生代的地质演化对于研究古特提斯洋关闭和冈瓦纳大陆解体都具有重要的指示意义。为查明羌塘盆地中生代的演化过程,在南、北羌塘坳陷上三叠统扎拉组和土门格拉组地层中共采集200余件砂岩样品进行古地磁对比研究。热退磁实验显示,大部分样品均含有两个磁组分,并揭示出一组高温特征剩磁分量,在95%置信度下通过正倒转检验和正褶皱检验,说明这组高温分量很可能代表岩石形成时的原生剩磁。南、北羌塘坳陷中样品的平均特征剩磁方向分别为D/I=28°/45.5°(a95=3.6°)和D/I=35.3°/46.5°(a95=4.0°);其相近的古地磁极和古纬度表明,南、北羌塘在晚三叠世已经属于一个统一的地块,并且具有北纬27°的古纬度。再结合前人研究成果发现,羌塘盆地晚古生代位于南半球中纬度地区,晚二叠世时已靠近赤道,并逐渐从冈瓦纳大陆北缘裂解开来向北漂移。羌塘盆地与塔里木地块在晚三叠世实现了碰撞拼合;中白垩世时,又与拉萨地块完成了板块碰撞。至此,羌塘盆地与周缘各地块基本上完成了碰撞拼合。The Qiangtang terrane is located in the central part of the Tibetan Plateau,where the Mesozoic geological evolution has great significance for revealing the closure of Paleotethyan ocean and the disintegration of Gondwanaland.In order to find out the Mesozoic evolution of the Qiangtang terrane,more than 200 paleomagnetic samples were collected from the Upper Trassic Tumengela Formation and Zala Formation both in the north and in the south Qiangtang.Most samples contained two components of magnetization in thermal demagnetization experiments.The most stable high-unblocking temperature components were isolated and passed positive reversal tests at the 95% confidence level,which suggested that these high-temperature components could be regarded as primary characteristic remanent magnetization.The mean characteristic magnetization directions of the samples from north Qiangtang and south Qiangtang were D/I=28°/45.5°（a95=3.6°） and D/I=35.3°/46.5°（a95=4.0°）,respectively.Nearly similar paleomagnetic polar and palaeolatitude,obtained from the north Qiangtang and the south Qiangtang,indicated that they had already belonged to one plate in the Late Triassic.The Late Triassic paleolatitude of Qiantang terrane was 27° in the Northern Hemisphere.Combined with previously reported paleomagnetic results,the paleomagnetic polar wandering paths were obtained.According to the paleomagnetic polar wandering paths,the Qiangtang terrane was located in the Southern Hemisphere during the Late Paleozoic and very close to the Equator in Late Permian.It drifted fast northward from the northeast Gondwanaland from the Late Paleozoic to the Mesozoic.The Qiangtang-Tarim plate collision finished at the end of the Triassic,and the Qiangtang-Lhasa collision might finish in the Middle Cretaceous.By then,all suture movements between Qiangtang terrane and other blocks had finished.

关 键 词：青藏高原 羌塘盆地 三叠纪 古地磁 构造 

分 类 号：P631.2[天文地球—地质矿产勘探]