昌都地块二叠纪那益雄组火山岩古地磁研究

发布时间：2019-03-21 17:25

【摘要】：羌北—昌都地块在现今构造格局表现为被北西—南东向的北澜沧江断裂带分割为两个相对独立的地块,两地块是由统一的地块经后期改造形成,还是由两个相对独立的地块运动拼合而成统一的羌北地块,目前尚无定论,因此,羌北块体与昌都块体的古地理位置与构造演化是研究青藏高原大地构造演化的关键问题之一。其中,晚古生代到早中生代是羌北块体与昌都块体地质演化的关键时期,这一时期的古地磁数据可以为研究羌北—昌都地块的形成演化提供依据。但是到目前为止,这两个块体的古地磁数据较少。本文以大地构造区划上属昌都地块的青海省格尔木市唐古拉山乡周琼玛鲁二叠纪那益雄组火山岩为研究对象,设置有效采点30个,采集定向样品252块,通过研究获得该地区的古地磁数据。岩石磁学研究表明,那益雄组火山岩的含磁性矿物主要为磁铁矿,还有一部分赤铁矿和针铁矿的存在。由此设定合理的退磁方案,通过系统热退磁方法对每块样品进行磁清洗并进行剩磁测定,再用Kirschvink主分量分析法与Fisher统计法对获得的剩磁信息进行分析与统计,得到样品的高温特征剩磁分量。获得的那益雄组(单斜层)高温分量与时代大体相当的九十道班组数据进行对比,通过了99%置信水平的褶皱检验,表明那益雄组高温分量很有可能代表原生剩磁信息。大部分样品呈现负极性特征,进一步验证了原生剩磁信息形成于晚二叠世。那益雄组高温特征剩磁分量平均方向为Ds=272.9°,Is=20.4°,Ks=32.3,α95=4.7°,其相应的古地磁极位置为纬度λ＝-8.2°,经度φ=189.1°,dp/dm=4.9/2.6,古纬度Φ=-10.5°。通过与本课题组之前所得数据的对比分析认为,中二叠世到晚二叠世昌都地块发生了8.5+13°的北向漂移,同时伴随有14.9±13.5°的逆时针旋转,此时其古纬度仍然位于南半球,对比羌北与昌都地块数据可以发现,此时他们的古纬度差为50左右；晚二叠世到晚三叠世期间,羌北地块与昌都地块都发生了北向漂移和逆时针旋转,并于晚二叠世末到早三叠世初碰撞形成统一的羌北—昌都地块。
[Abstract]:The present tectonic pattern of the Qiang-Changdu block is divided into two relatively independent blocks by the north-west-south-east-trending north Lancang river fault zone, and the two blocks are formed by the later transformation of the unified block. At present, there is no definite conclusion that the paleogeographic position and tectonic evolution of the North Qiang block and Changdu block are one of the key problems in studying the tectonic evolution of the Qinghai-Xizang Plateau. Among them, the late Paleozoic to early Mesozoic is the key period of geological evolution of the North Qiang block and Changdu block. The paleomagnetic data of this period can provide a basis for the study of the formation and evolution of the Qiangbei-Changdu block. But up to now, the paleomagnetic data of these two blocks are less. In this paper, the volcanic rocks of the Permian Nayixiong formation, Zhouqiongmalu, Tanggula Mountain Township, Golmud City, Qinghai Province, which belong to the Changdu block in geotectonic regionalization, are studied, and 30 effective mining sites are set up, and 252 directional samples are collected. The paleomagnetic data of the area are obtained through the study. The study of lithomagnetism shows that the magnetic minerals in the volcanic rocks of the Nayixiong formation are mainly magnetite and some hematite and goethite exist. Therefore, a reasonable demagnetization scheme is set up, each sample is cleaned by systematic thermal demagnetization method and the remanence magnetic field is measured, and then the remanent magnetic information obtained is analyzed and counted by Kirschvink principal component analysis and Fisher statistical method. The characteristic magnetic remanence component at high temperature is obtained. The high temperature component of Nayixiong formation (monoclinal layer) is compared with that of Nayixiong formation, which is about the same age, and the fold test at 99% confidence level shows that the high temperature component of Nayixiong formation is likely to represent the primary remanence information. Most of the samples show negative polarity, which further verifies that the primary remanence information was formed in the late Permian. The mean direction of high temperature characteristic remanent magnetic component of Nayixiong group is Ds=272.9 掳, Is=20.4 掳and Ks=32.3, 伪 95 掳. The corresponding paleomagnetic pole position is latitude 位 =-8.2 掳, longitude 蠁 = 189.1 掳, dp/dm=4.9/2.6,. The ancient latitude 桅 =-10.5 掳. Through the comparison and analysis of the data obtained by our research group, it is concluded that the middle Permian to late Permian Changdu block experienced a northward drift of 8.5 13 掳, accompanied by a counter-clockwise rotation of 14.9 卤13.5 掳. At this time, its ancient latitude is still located in the southern hemisphere, compared with the north of Qiang and Changdu block data can be found, at this time their paleo-latitude difference is about 50; From late Permian to late Triassic, both Qiangbei block and Changdu block occurred northward drift and counterclockwise rotation, and formed a unified Qiangbei-Changdu block by collision from late Permian to early Triassic.
【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】：P588.14;P318.44

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