青藏高原羌北—昌都地块晚二叠世那益雄组火山岩锆石U-Pb年代学及古地磁学研究

发布时间：2018-03-06 01:18

  本文选题：青藏高原　切入点：羌北-昌都地块　出处：《西北大学》2017年硕士论文　论文类型：学位论文

【摘要】：羌北-昌都地块是青藏高原腹地面积较大、具有古老基底且古生代以来的沉积盖层发育相对齐全的稳定块体之一。确定出其晚古生代的古地理位置对于研究青藏高原冈瓦纳与欧亚大陆界线、古特提斯洋演化以及古大陆重建等都具有重要意义。本文对青海省格尔木市唐古拉山乡阿布日阿加措地区晚二叠世那益雄组火山岩地层开展岩石学、锆石U-Pb年代学、岩石磁学和古地磁学研究工作,并与沉积地层中获得古地磁数据进行比较分析,获得了羌北-昌都地块一个有精确年龄控制的可靠古地磁数据,重建这一关键块体晚二叠世的古地理位置并探索了羌北-昌都地块及其周边地块的古位置关系。通过对研究区那益雄组地层剖面手标本观察、薄片鉴定及主微量元素测试分析,可以将研究剖面分为三段:上段为深灰色流纹岩,中段为灰绿色、灰色凝灰岩,下段为紫红色、红褐色玄武岩,安山岩。对那益雄组地层上段流纹岩,下段安山岩分别采取一件样品进行锆石U-Pb同位素年龄测定,得出流纹岩加权平均年龄值为249.6±1.3Ma,安山岩加权平均年龄值为251.1±4.8Ma,测年结果显示,那益雄组这套地层形成于250Ma左右,即晚二叠世。对晚二叠世那益雄组地层设置39个采点采集309块定向样品。8个代表性样品的岩石磁学研究显示,流纹岩样品主要载磁矿物为磁铁矿和赤铁矿;凝灰岩样品主要载磁矿物为磁铁矿;玄武岩、安山岩样品主要载磁矿物为赤铁矿。309块样品磁化率各向异性实验也表明那益雄组地层没有经受过强烈的变形和压实作用。对晚二叠世那益雄组39个采点309块样品经过系统的热退磁实验及详细的数据分析比较,最终对36个采点(采点合并后30个)253块样品的高温分量进行统计,得出高温特征剩磁方向经过倾斜校正后Ds=274.8°,Is=23.2°,Ks=27.9,α95=5.1°,所对应的古地磁极位置为-10.6°N,189.4°E,A95=4.0°,相对于参考点(33.87°N,91.92°E),古纬度为-12.1°N。本文引用程鑫等人发表九十道班组数据与研究区那益雄组数据做广义的褶皱检验,两组数据的高温特征剩磁分量通过褶皱检验。高温分量方向均表现为反极性(正倾角),与Kiaman负极性段(KRS)相吻合,以上结果表明高温特征剩磁分量代表了岩石的原生剩磁。VGP离散度检验表明,火山岩数据平均掉了地磁场长期变化的影响。根据以上研究结果,相对于参考点(33.87°N,91.92°E),我们判定出羌北-昌都地块250Ma左右时位于南纬12.1°左右。结合古生物资料,岩石学证据及前人对羌北-昌都周边板块所做古地磁研究,绘制出了羌北-昌都地块及周边块体晚二叠世古地理重建图。
[Abstract]:The northern Qiang and Changdu blocks have a relatively large area in the hinterland of the Qinghai-Tibet Plateau. One of the stable blocks with an ancient basement and relatively complete sedimentary caprocks since Paleozoic. The paleogeographic location of the late Paleozoic has been determined for the study of the boundary between Gondwana and Eurasia on the Qinghai-Xizang Plateau. The evolution of the PaleoTethys ocean and the reconstruction of the ancient continent are of great significance. This paper has developed petrology and zircon U-Pb geochronology for the volcanic strata of the late Permian Yishong formation in the Tanggulashan Township of Golmud City, Qinghai Province. A reliable paleomagnetic data with precise age control has been obtained from rock magnetism and paleomagnetism, which is compared with paleomagnetic data obtained from sedimentary strata. The paleogeographic location of the key block in the late Permian period was reconstructed and the paleo-location relationship of the Qiangbei-Changdu block and its surrounding block was explored. Through the observation of the hand specimen of the stratigraphic section of the Nayixiong formation in the study area, the identification of the thin section and the analysis of the main and trace elements, The study profile can be divided into three sections: the upper segment is dark gray rhyolite, the middle section is gray-green, gray tuff, the lower part is purplish red, reddish brown basalt, andesite. The zircon U-Pb isotopic age of the lower member andesite is determined by one sample, and the weighted mean age of rhyolite is 249.6 卤1.3 Ma.The weighted average age of the andesite is 251.1 卤4.8 Ma.The dating results show that the formation of the Nayixiong formation was formed at about 250 Ma. That is, the late Permian. 309 directional samples were collected from 39 mining sites of the late Permian Yi-hsiung formation. The magnetomagnetic studies of 8 representative samples show that the magnetite and hematite are the main magnet-carrying minerals in the rhyolite samples. The main magnetite bearing minerals in tuff samples are magnetite, basalt, The magnetic susceptibility anisotropy experiment of andesite sample is mainly hematite. 309 samples from 39 mining sites of the late Permian Shinayixiong formation are not subjected to strong deformation and compaction. After systematic thermal demagnetization experiments and detailed data analysis and comparison, Finally, the high temperature components of 36 sampling points (30 samples of Cu 253 after the combination of the sampling points) were counted. The results show that the direction of remanent magnetization of high temperature is corrected by tilting Ds=274.8 掳Isan = 23.2 掳KsN 27.9, 伪 95N 5.1 掳, and the corresponding paleomagnetic pole position is -10.6 掳Nou 189.4 掳EKA 95N 4.0 掳, relative to the reference point of 33.87 掳Nai 91.92 掳E, paleolatitude is -12.1 掳N. Cheng et al., et al., published 90 shift group data and the data of Nayixiong formation in the study area. Generalized fold test, The high temperature characteristic remanent magnetic components of the two sets of data are tested by fold test. The direction of the high temperature components are all in reverse polarity (positive dip angle), which coincides with the Kiaman negative polarity segment KRSs. The above results show that the high temperature characteristic remanent magnetic component represents the primary remanence of rock. VGP dispersion test shows that the volcanic rock data have lost the influence of the long-term variation of geomagnetic field on average. In contrast to the reference point of 33.87 掳Nian 91.92 掳E, we have determined that the Qiangbei Changdu block is located at about 12.1 掳south latitude at about 250 Ma. In combination with paleontological data, petrological evidence and paleomagnetic study of the plate around Qiangbei Qiang Qiang Qiang Chang du have been done by our predecessors. The paleogeographic reconstruction map of the northern Qiang-Changdu block and its surrounding block in late Permian was plotted.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P597.3;P318.44
，

本文编号：1572715