【作者】 谌微微；

【导师】 张世红；

【作者基本信息】 中国地质大学（北京） ， 构造地质学， 2014， 博士

【摘要】 青藏高原是由不同陆块由北到南依次拼贴到欧亚大陆之上组成，不同陆块间相互作用及旋转过程制约着各种地质事件的发生与发展。中生代以来的构造事件，包括羌塘与拉萨地块的拼贴、印度与欧亚大陆的碰撞，不仅使拉萨和欧亚大陆之间发生强烈构造缩短，还制约着中-新特提斯洋的演化过程。白垩纪期间羌塘与拉萨地块的碰撞拼合导致班公-怒江大洋的消失。目前，关于班公-怒江缝合带的性质、演化过程和闭合时间仍存在激烈争议。此外，白垩纪以来欧亚大陆内部的构造缩短量、陆块旋转模式和新特提斯洋规模等热点问题均存在争议。因此，羌塘和拉萨地块白垩纪期间的古地理位置成为研究板块构造演化和中-新特提斯洋演化的重要窗口。在对拉萨地块措勤地区则弄群火山岩古地磁研究的基础上，本论文在羌塘地块改则地区对白垩纪火山岩和红层展开系统的古地磁及年代学综合研究。改则火山岩样品U-Pb测年结果为103.8±0.46Ma，红层年龄为103.8-83.5Ma。经过系统热退磁，从改则地区火山岩和经过E/I校正后的红层中获得的古地磁极分别为79.3°N，339.8°E，A95=5.7°和49.5°N，2.6°E，A95=3.6°，支持羌塘地块103.8±0.46Ma期间位于29.3°N，10.4-83.5Ma期间位于相同的古纬度（29.2°N）。结合地质资料和前人在羌塘、拉萨地块获得的古地磁结果，本文结果支持班公湖-怒江大洋中西部闭合时间在103.8Ma附近，晚白垩期间羌塘和拉萨地块之间存在~580km的构造缩短；拉萨地块123.1Ma期间古纬度为20.1±4.8°N，与同期稳定欧亚大陆相比，二者存在9.8±4.1°古纬度差，除去晚白垩世期间羌塘和拉萨地块之间发生的构造缩短量，结果表明印度-欧亚大陆碰撞导致欧亚大陆内部发生了~500km的南北向构造缩短；早白垩世拉萨地块南缘和印度大陆北缘之间存在59.6±4.2°的古纬度差，意味着早白垩世期间印度板块与欧亚大陆之间的新特提斯大洋南北向规模达到6615.6±466km。此外，本文结合前人在青藏高原的研究结果（包括大量GPS数据和古地磁数据），支持青藏高原腹地白垩纪以来东西部经历不同旋转模式，东部发生显著的顺时针旋转，中西部发生逆时针旋转。不同区域由于走滑断层的发育导致旋转量的有所差异，但总体上符合上述规律，并且旋转的主要动力来自印度-欧亚大陆的剧烈碰撞。更多还原

【Abstract】 The Tibet Plateau was formed by progressive accretion of several terranes to thestable Asian migrated from north to south, the interaction and the rotation processbetween different terranes provide constraints on the occurrence of various geologicalevents. Tectonic events since the Mesozoic including the collage between the Qiangtangand Lhasa terranes and the collision of India and Eurasia, not only caused the intensecrustal shortening between the Lhasa terrane and the stable Eurasia, but also restrictedthe evolution process of the Mid-Neo Tethys. The Qiangtang and Lhasa terranescollided during the Cretaceous accompanying with the closure of the Bangong-Nujiangocean. At present, some key aspects about the Bangong-Nujiang ocean, such as itsnature of the ocean basin, its evolution and closed time are still open to intense debate.In addition, there has been no consensus on the crustal shortening, rotated model andthe scale of the Neo-Tethys. Therefore, the Cretaceous paleogeography of Qiangtangand Lhasa terranes has become an important window of studying the evolution of theterranes and the Mid-Neo Tethys.Base on the paleomagnetic study of the Zenong volcanics sampled from Cuoqinarea, a combined geochronological and paleomagnetic investigation has been performedon Cretaceous rocks in the west of the Qiangtang terrane near Gaize area. Ageochronologic study of zircon U-Pb dating indicates that the volcanic rocks sampledfrom the Gaize area is103.8±0.46Ma while the red beds belong to103.8-83.5Ma.After thermal demagnetization, the paleopoles obtained from the volcanic rocks and redbeds corrected by the E/I method are79.3°N,339.8°E, A95=5.7°and49.5°N,2.6°E,A95=3.6°, respectively. The results support that the Qiangtang terrane located at29.3°Nduring103.8-83.5Ma. Combined with the geological evidence and previouspaleomagnetic results from the Qiangtang and Lhasa terranes, this study support that thewestern segment of the Bangong-Nujiang ocean closed at~103.8Ma and~580kmcrustal shortening happened during the later Cretaceous. Comparing the paleolatitude ofthe southern margin of the Lhasa terrane (20.1°±4.8°N) with the stable Asia at120Ma,the significant discrepancy (9.8±4.1°) implies that~500km N-S crustal shortening has taken place between them caused by the India-Asia collision which has excluded thecontribution of the Qiangtang-Lhasa terranes collision. Comparing the paleolatitudesbetween stable India and the Lhasa terrane, the paleolatitude difference is59.6±4.2°,indicating the width for the Neotethys ocean was6615.6±466km in the earlyCretaceous. Besides, combined the previous studies (including GPS data andpaleomagnetic data), this study supports that the hinterland of the Tibet plateauexperienced different rotation models from the east to the west since the Cretaceous.The southeast of the Tibet plateau has experienced a large scale clockwise while asignificant count-clockwise rotation happened in the mid-west part. Although theamount of rotation in different regions may be vary influenced by the development ofthe strike-slip faults, they agree with the above rotation models in general mainlytrigged by the India-Asia collision.更多还原