本文選題：青藏高原　切入點：羌北-昌都地塊　出處：《西北大學》2017年碩士論文　論文類型：學位論文

【摘要】：羌北-昌都地塊是青藏高原腹地面積較大、具有古老基底且古生代以來的沉積蓋層發(fā)育相對齊全的穩(wěn)定塊體之一。確定出其晚古生代的古地理位置對于研究青藏高原岡瓦納與歐亞大陸界線、古特提斯洋演化以及古大陸重建等都具有重要意義。本文對青海省格爾木市唐古拉山鄉(xiāng)阿布日阿加措地區(qū)晚二疊世那益雄組火山巖地層開展巖石學、鋯石U-Pb年代學、巖石磁學和古地磁學研究工作,并與沉積地層中獲得古地磁數(shù)據(jù)進行比較分析,獲得了羌北-昌都地塊一個有精確年齡控制的可靠古地磁數(shù)據(jù),重建這一關(guān)鍵塊體晚二疊世的古地理位置并探索了羌北-昌都地塊及其周邊地塊的古位置關(guān)系。通過對研究區(qū)那益雄組地層剖面手標本觀察、薄片鑒定及主微量元素測試分析,可以將研究剖面分為三段:上段為深灰色流紋巖,中段為灰綠色、灰色凝灰?guī)r,下段為紫紅色、紅褐色玄武巖,安山巖。對那益雄組地層上段流紋巖,下段安山巖分別采取一件樣品進行鋯石U-Pb同位素年齡測定,得出流紋巖加權(quán)平均年齡值為249.6±1.3Ma,安山巖加權(quán)平均年齡值為251.1±4.8Ma,測年結(jié)果顯示,那益雄組這套地層形成于250Ma左右,即晚二疊世。對晚二疊世那益雄組地層設(shè)置39個采點采集309塊定向樣品。8個代表性樣品的巖石磁學研究顯示,流紋巖樣品主要載磁礦物為磁鐵礦和赤鐵礦;凝灰?guī)r樣品主要載磁礦物為磁鐵礦;玄武巖、安山巖樣品主要載磁礦物為赤鐵礦。309塊樣品磁化率各向異性實驗也表明那益雄組地層沒有經(jīng)受過強烈的變形和壓實作用。對晚二疊世那益雄組39個采點309塊樣品經(jīng)過系統(tǒng)的熱退磁實驗及詳細的數(shù)據(jù)分析比較,最終對36個采點(采點合并后30個)253塊樣品的高溫分量進行統(tǒng)計,得出高溫特征剩磁方向經(jīng)過傾斜校正后Ds=274.8°,Is=23.2°,Ks=27.9,α95=5.1°,所對應(yīng)的古地磁極位置為-10.6°N,189.4°E,A95=4.0°,相對于參考點(33.87°N,91.92°E),古緯度為-12.1°N。本文引用程鑫等人發(fā)表九十道班組數(shù)據(jù)與研究區(qū)那益雄組數(shù)據(jù)做廣義的褶皺檢驗,兩組數(shù)據(jù)的高溫特征剩磁分量通過褶皺檢驗。高溫分量方向均表現(xiàn)為反極性(正傾角),與Kiaman負極性段(KRS)相吻合,以上結(jié)果表明高溫特征剩磁分量代表了巖石的原生剩磁。VGP離散度檢驗表明,火山巖數(shù)據(jù)平均掉了地磁場長期變化的影響。根據(jù)以上研究結(jié)果,相對于參考點(33.87°N,91.92°E),我們判定出羌北-昌都地塊250Ma左右時位于南緯12.1°左右。結(jié)合古生物資料,巖石學證據(jù)及前人對羌北-昌都周邊板塊所做古地磁研究,繪制出了羌北-昌都地塊及周邊塊體晚二疊世古地理重建圖。
[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 鹵1.3 Ma.The weighted average age of the andesite is 251.1 鹵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 擄Isan = 23.2 擄KsN 27.9, 偽 95N 5.1 擄, and the corresponding paleomagnetic pole position is -10.6 擄Nou 189.4 擄EKA 95N 4.0 擄, relative to the reference point of 33.87 擄Nai 91.92 擄E, paleolatitude is -12.1 擄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 擄Nian 91.92 擄E, we have determined that the Qiangbei Changdu block is located at about 12.1 擄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.
【學位授予單位】：西北大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P597.3;P318.44
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本文編號：1572715