古地磁综述:青藏高原东北的旋转变形

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• 作者：颜茂都方小敏宋春晖张伟林
• 会议时间：2014-10-19
• 关键词：青藏高原 ; 旋转变形 ; 古地磁结果 ; 地球动力学模型
• 作者单位：颜茂都,方小敏,张伟林(中国科学院青藏高原研究所大陆碰撞和高原隆升重点实验 北京 100101)宋春晖(兰州大学地质科学与矿产资源学院学 兰州 730000)
• 母体文献：2014年中国地球科学联合学术年会论文集
• 会议名称：2014年中国地球科学联合学术年会
• 会议地点：北京
• 主办单位：中国地球物理学会
• 语种：chi
• 分类号：P31

摘要

Paleomagnetism can quantitative determine tectonic rotations around a vertical axis and test geodynamic models concerning the kinematics of the India-Asia collision.However,so far paleomagnetic studies in the northeastern (NE) Tibetan Plateau are still difficult to relate tectonic rotations to regional geodynamics,due to poor age control and some discordant paleomagnetic results on the studied rocks.For example,paleomagnetic data from the west NE Tibetan Plateau are contradictory,in that they are being used as arguments for significant (clockwise or counterclockwise) and insignificant rotations of the region;whereas data from east of the plateau are marred by a lack of comprehensive understanding as to the timing and geographic distribution of significant clockwise rotations of ~25 degree,such as mid-Miocene rotations of the Guide Basin and Eocene-Oligocene rotations of the Longzhong Basin.Recent three magnetostratigraphic based rotation studies around the NE Tibetan Plateau has successfully revealed rotation variations through time (Wang et al.,2011;Yan et al.,2012;Zhang et al.,2012),all indicating existences of multiple rotation patterns during the late Neogene.Given recent large amount of magnetostratigraphic results and the possible existence of multiple changes in the sense and magnitude of rotation of the northeast Tibetan Plateau during Neogene,average declinations were calculated for every 100m of well dated magnetostratigraphy sections from the Kunlun,Qaidam,Chaka,Linxia,Tianshui and Liupanshan basins,combined with the published results of the Jiuquan and Guide basins,to discuss the Neogene rotations of the northeast Tibetan Plateau.The analyses indicate that significant rotations did exist around the northeast Tibetan Plateau:(1)an overall pattern of clockwise rotation within the northeast Tibetan Plateau,but more or less counterclockwise rotation outside of the plateau;(2)significant rotations since~11-8Ma,and with accelerated rotations or switch of rotation patterns since ~5-3Ma;and(3)the magnitude of clockwise rotations decreases from the west(Qaidam and Guide Basins) of ~25°to the east (Linxia and Tianshui Basins)of ~10°,while those outside of the NE Tibetan Plateau or close to the major faults the magnitude is generally large(>20°-30°)and with some complicated rotation history。