【摘要】：青藏高原屬于特提斯構(gòu)造域東段,羌塘地塊是青藏高原的主要地體,研究羌塘地塊對其構(gòu)造演化及運動學(xué)、動力學(xué)等問題至關(guān)重要,其形成演化涉及到古特提斯洋的關(guān)閉和新特斯洋的開啟等地學(xué)熱點問題。本次研究以羌塘地塊北部的唐古拉山地區(qū)的中生代地層為目的層,該剖面地層時代清楚,地層接觸關(guān)系確定。以期望通過該區(qū)中生代地層的古地磁研究為羌塘地塊的大地構(gòu)造演化以及新特提斯洋的形成提供定量約束。本次研究在羌塘地塊北部的唐古拉山地區(qū)共設(shè)置了15個采樣點,其中晚三疊世結(jié)扎群設(shè)置采點9個,采集107塊定向標(biāo)本,早白堊世錯居日組設(shè)置采點6個,共43塊定向標(biāo)本,共采集150塊古地磁定向樣品。在室內(nèi)將其加工成標(biāo)樣,在中科院地質(zhì)與地球所古地磁與年代學(xué)實驗室進行了巖石磁學(xué)和退磁實驗。晚三疊世結(jié)扎群沉積巖地層通過其巖石磁學(xué)研究發(fā)現(xiàn),主要攜磁礦物為赤鐵礦、磁黃鐵礦、少量鈦磁鐵礦、極少量的磁鐵礦。早白堊世錯居日組紫紅色細(xì)砂巖的主要攜磁礦物是赤鐵礦,還有少量針鐵礦。根據(jù)磁性礦物類型,制定了合適的退磁方法和退磁實驗步驟,對樣品有針對性的進行了系統(tǒng)的熱退磁,交變退磁和混合退磁等實驗。對剩磁數(shù)據(jù)分析采用了kirschvink主分量分析法,對采點內(nèi)和地層組水平上數(shù)據(jù)統(tǒng)計采用Fisher統(tǒng)計,晚三疊世結(jié)扎群沉積巖樣品的高溫分量通過了McElhiny褶皺檢驗,早白堊世錯居日組細(xì)砂巖樣品高溫分量通過了倒轉(zhuǎn)檢驗,均可被認(rèn)為是原生剩磁分量。通過以上實驗和分析統(tǒng)計及計算,得出結(jié)扎群沉積巖組的高溫剩磁分量平均方向為：Ds=4.2°,Is=-29.7°, Ks=24, α95=10.7°;計算出相應(yīng)的古地磁極位置為：φp=259.4°, λp=71.5°, dp/dm=8.8°;古緯度為Φ古=15.9°N；錯居日組的高溫剩磁分量平均方向為：Ds=154.8°,Is=-43.2°, Ks=19.2, α95=15.7°;計算出相應(yīng)的古地磁極位置為：λp=66.3°,λP=346.2°, dpldm=15.4°,古緯度為Φ古=25.2°N。根據(jù)本次研究得到的最新古地磁數(shù)據(jù),并結(jié)合前人對拉薩地塊的研究成果,進行了對比討論,并繪制了羌塘和拉薩的石炭紀(jì)到白堊紀(jì)的視極移曲線(APWP)圖和古緯度變化圖。得出以下結(jié)論：晚三疊世班公湖-怒江洋縫合帶所代表的新特提斯洋擴張到最大,羌塘(Φ古=15.9)和拉薩(Φ古=-16.6)兩者緯度最大相差至少32.5°,指示了班怒洋此時的規(guī)模至少有3600km,此后該洋盆開始收縮。從APWP可知,從晚三疊世到中晚侏羅世,羌塘板塊表現(xiàn)出了較明顯的“極移”現(xiàn)象,并且快速的向北漂移,說明該時期是羌塘板塊的快速北移時期。中晚侏羅到早白堊世,羌塘地塊緯向漂移量顯著減少,主要是逆時針旋轉(zhuǎn)期。根據(jù)拉薩和羌塘地塊在此時的視極移曲線與古緯度的分析,指示中侏羅世拉薩地塊的北移,使得其北的班公湖-怒江洋閉合。
[Abstract]:The Qinghai-Tibet Plateau belongs to the eastern segment of the Tethys tectonic domain, and the Qiangtang block is the main terrane of the Qinghai-Tibet Plateau. It is important to study the Qiangtang block for its tectonic evolution, kinematics and dynamics. Its formation and evolution related to the closure of the ancient Tethys Ocean and the opening of the New Tethys Ocean. The Mesozoic strata in Tanggula Mountain area in the north of Qiangtang block are taken as the target layer. The stratigraphic age of the section is clear and the stratigraphic contact relationship is determined. The paleomagnetic study of Mesozoic strata in this area is expected to provide quantitative constraints for the tectonic evolution of the Qiangtang block and the formation of the NeoTethys Ocean. In this study, 15 sampling sites were set up in Tanggula Mountain area in the north of Qiangtang block, of which 9 were collected in late Triassic ligation group, 107 directional specimens were collected, and 6 were collected in early Cretaceous staggered Jourri formation, with 43 directional specimens. A total of 150 paleomagnetic directional samples were collected. The lithomagnetic and demagnetization experiments were carried out in the paleomagnetism and geochronology laboratory of the Institute of Geomagnetism and Geochronology of the Chinese Academy of Sciences. The sedimentary strata of the late Triassic Lianza Group found that the main magnetic carrying minerals are hematite, pyrrhotite, a small amount of ilmenite and a very small amount of magnetite. In the early Cretaceous Miaojuri formation, the main magnetic carrying minerals of the fuchsia fine sandstone are hematite and a small amount of goethite. According to the type of magnetic minerals, the appropriate demagnetization method and demagnetization experimental steps were established, and systematic experiments such as thermal demagnetization, alternating demagnetization and mixed demagnetization were carried out on the samples. Kirschvink principal component analysis was used to analyze the residual magnetic data, Fisher was used to statistics the data in the production point and stratigraphic group, and the high temperature component of the sedimentary rock samples of the late Triassic ligation group passed the McElhiny fold test. The high temperature components of the early Cretaceous Miaojuri formation fine sandstone have passed the inversion test and can be considered as primary remanent magnetic components. Based on the above experiments, statistics and calculations, it is obtained that the mean direction of the high-temperature remanent magnetic components of the sedimentary rocks in the Lianzhang Group is: 1: Dsl 4.2 擄Is-29.7 擄, KsN 24 擄, 偽 9510 7 擄, and the corresponding paleomagnetic pole positions are: 蠁 p0 259.4 擄, 位 p0 71.5 擄, dp/dm=8.8 擄, and 桅 paleo (15.9 擄N). The mean direction of the high temperature remanent magnetic component in the staggered group is: 1 DsN 154.8 擄Is-43.2 擄, Ksl 19.2 擄, 偽 95N 15.7 擄, and the corresponding paleomagnetic pole positions are calculated as 位 PU 66.3 擄, 位 PU 346.2 擄, dpldm=15.4 擄, and paleolatitude 桅 paleo 25.2 擄N. Based on the latest paleomagnetic data obtained in this study and combined with the previous research results of Lhasa block, this paper makes a comparative discussion, and draws the (APWP) diagram of the Carboniferous to Cretaceous apparent pole shift curve and the paleolatitude variation map of Qiangtang and Lhasa. The following conclusions are drawn: the Neo-Tethys ocean represented by the late Triassic Bangong Lake-Nu River ocean suture zone expanded to the largest extent. The maximum latitudes difference between Qiangtang (桅 Guji15.9) and Lhasa (桅 Guji-16.6) is at least 32.5 擄, indicating that the scale of Banru Ocean is at least 3600km at this time, and then the basin begins to shrink. According to APWP, from the late Triassic to the Middle and late Jurassic, the Qiangtang plate showed a more obvious "pole shift" phenomenon, and the rapid northward drift, indicating that this period is a period of rapid northward migration of the Qiangtang plate. From the middle late Jurassic to the early Cretaceous, the zonal drift of Qiangtang block decreased significantly, mainly in the counterclockwise rotation period. According to the analysis of the apparent pole shift curve and paleo latitude of Lhasa and Qiangtang blocks at this time, it is indicated that the northward migration of Lhasa block in the Middle Jurassic resulted in the closure of the Bangong Lake and the Nujiang River in the north of Lhasa and Qiangtang blocks.
【學(xué)位授予單位】：西北大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P318.44;P534.5

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