羌南下石炭统日湾擦卡组古地磁研究

发布时间：2018-06-19 17:30

本文选题：羌南地块 + 日湾擦卡组　；参考：《西北大学》2015年硕士论文

【摘要】：羌塘地块对于青藏高原的演化及动力学等问题的研究至关重要。羌塘地块曾被认为是一个整体,直到双湖-龙木错缝合带的发现,羌塘地块被划分为羌北和羌南两个块体,同时,也将冈瓦纳大陆和欧亚大陆界线问题的分歧集中到班公湖—怒江缝合带及双湖—龙木错缝合带二者之间,因此,羌南地块之北的双湖—龙木错缝合带在晚古生代到底是不是欧亚大陆的南缘,也即在晚古生代羌南和羌北是否已拼合这一问题至关重要。那么,羌南以及羌北块体晚古生代的古地磁数据对研究这一问题就显得十分重要。但是目前只有羌北地块获得的古地磁数据比较充分,而羌南地块的古地磁数据特别是晚古生代的数据十分稀少,这使得龙木错一双湖缝合带演化时限的确定比较困难。针对这一问题,本文选择羌南地块下石炭统的日湾擦卡组地层进行古地磁研究,以期获得早石炭世羌南地块的古地磁极位置及古纬度,为青藏高原大地构造演化研究提供依据。在羌南地块改则地区下石炭统的日湾擦卡组地层设置12个采样点,共采集167块野外古地磁定向样品,室内加工后对其进行岩石磁学研究和退磁处理。岩石磁学结果显示岩石中载磁矿物主要包括磁铁矿和针铁矿,还有少量磁黄铁矿。由此,对于实验样品采用热退磁、交变退磁以及混合退磁方法进行磁清洗,采用主分量分析方法进行分析并用Fisher统计法对样品的剩磁进行统计,分别获得低温分量和高温分量的平均方向。其低温分量方向与现代地磁场方向近于相同,可能是现代地磁场重磁化的结果；高温分量结果则通过了严格的褶皱检验,很可能代表了原生剩磁。本文获得下石炭统日湾擦卡组地层校正后的高温分量平均方向为：Ds=242°, Is=18.8°,Ks=19.9,a95=10°:对应的古地磁极位置为：γp=16.9°,ψp=199.1°, dp/dm=10.4/5.4；古纬度西古一9.7。。通过与羌北地块同时代的古地磁极位置对比可以得知：石炭纪时,羌南地块处于南半球,并且和羌北地块处于分离状态,没有拼合,因此可以认为在石炭纪时特提斯洋位于羌北地块和羌南地块之间。结合前人资料分析可以推断羌南地块和羌北地块在晚二叠世拼合形成整体的羌塘地块,双湖-龙木错缝合带不再是欧亚大陆的南缘,羌塘块体之南的班公湖-怒江带成为新的欧亚大陆南缘。羌南块体在石炭纪到三叠纪的运动趋势总体北移并伴随有旋转。
[Abstract]:The Qiangtang block is very important for the study of the evolution and dynamics of the Qinghai-Tibet Plateau. The Qiangtang block was once considered as a whole until the discovery of the Shuanghu-Longmu dislocation suture zone. The Qiangtang block was divided into two blocks, the northern Qiang and the southern Qiang, and at the same time, The differences between Gondwana and Eurasia are also concentrated between the Bangong Lake-Nujiang suture zone and the Shuanghu-Longmu fault suture zone. Whether the Shuanghu-Longmu fault suture belt in the northern part of the southern Qiang block is the southern edge of Eurasia in the late Paleozoic, that is, whether the southern Qiang and the northern Qiang in the late Paleozoic have been combined or not is of great importance. The paleomagnetic data of the late Paleozoic in the southern Qiang and northern Qiang blocks are very important for the study of this problem. But at present, only the paleomagnetic data obtained from the northern Qiang block are quite sufficient, and the paleomagnetic data of the southern Qiang block are very rare especially in the late Paleozoic, which makes it difficult to determine the time limit for the evolution of the Longmu dislocation Shuanghu suture zone. In order to obtain the paleomagnetic pole position and paleolatitude of the early Carboniferous Qiangnan block, this paper chooses the lower Carboniferous strata of the Lower Carboniferous to study paleomagnetism in order to provide the basis for the study of tectonic evolution of the Qinghai-Xizang Plateau. A total of 167 field paleomagnetic directional samples were collected at 12 sampling points in the lower Carboniferous strata of the Lower Carboniferous in the Changzi area of the Qiang Nan Block. The rock magnetics and demagnetization were studied and demagnetized after laboratory processing. The results of petromagnetism show that there are mainly magnetite and goethite, and a small amount of pyrrhotite. Therefore, the experimental samples were cleaned by thermal demagnetization, alternating demagnetization and mixed demagnetization. Principal component analysis (PCA) and Fisher statistics were used to analyze the remanence of the samples. The average directions of the low temperature component and the high temperature component are obtained respectively. The direction of the low-temperature component is similar to that of the modern geomagnetic field, which may be the result of the gravity magnetization of the modern geomagnetic field, while the high-temperature component results pass the strict fold test, which probably represents the primary remanence. In this paper, the average direction of high temperature component after stratigraphic correction in the Lower Carboniferous Zhiwan Zaika formation is found to be: 1: Dsn 242 掳, Iso 18.8 掳KS ~ (19. 9) a 95 ~ 10 掳: the corresponding paleomagnetic pole position is 纬 p ~ (16. 9) 掳, 蠄 ~ (p) 199.1 掳, DP / D ~ (m) 10.4 / 4, and paleolatitude is 9. 7. 7. By comparing the paleomagnetic pole position of the same age with the northern Qiang block, it can be concluded that the southern Qiang block was in the southern hemisphere during the Carboniferous, and it was separated from the northern Qiang block, and there was no combination. Therefore, the Tethys Ocean was located between the northern Qiang block and the southern Qiang block during the Carboniferous. Based on the analysis of previous data, it can be inferred that the southern Qiang block and the northern Qiang block combined to form a whole Qiangtang block in the late Permian, and the Shuanghu-Longmu fault suture zone is no longer the southern margin of Eurasia. The Bangong Lake-Nujiang belt to the south of the Qiangtang block became the southern edge of the new Eurasian continent. The movement trend of the southern Qiang block from Carboniferous to Triassic generally moved northward and was accompanied by rotation.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P318.44;P534.45

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