【作者】 裴军令；

【导师】 杨振宇； 赵越；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2008， 博士

【摘要】 研究区位于华北地块北缘的燕山褶断带,是中国地质工作的摇篮,以中新生代强烈的板内变形闻名于世。从上个世纪初开始,国内外学者就这一地区中新生代的地质与构造问题开展了大量的研究工作,取得了许多重要的认识。近年来,随着对燕山地区中生代地层相关问题的深入研究,取得了大量新的研究成果。但是,对燕山褶断带中生代地层时代的划分和构造过程等尚有诸多争论和问题有待进一步澄清。本文选择对燕山褶断带东段冀北滦平盆地早白垩世地层进行了古地磁学和SHRIMP锆石U-Pb年代学研究。滦平盆地三道沟剖面大北沟组-大店子组沉积序列完整、出露完全、化石丰富。通过该剖面的磁性地层学研究,建立了冀北大北沟组-大店子组-西瓜园组磁极性序列。利用SHRIMP锆石U-Pb测年方法,获得了滦平盆地大店子组顶部火山凝灰岩的时代为131±6 Ma。综合大北沟组-大店子组-西瓜园组高精度磁性地层学研究结果与生物地层、岩石地层、年代地层及层序地层成果,对大北沟组-大店子组-西瓜园组下部的时限进行了初步划分。为冀北及国内相关地层单元的时代划分与对比提供了基础资料。本文初步认为Aptian/Barremian年龄为120 Ma、Barremian/Hauterivian年龄为125.1 Ma、Hauterivian/Valanginian年龄为130.4 Ma。对比方案Ⅲ中提出大北沟组属于Valanginian早期,大店子组主体上属于Valanginian中晚期,西瓜园组下部则对应Valanginian/Hauterivian界线附近。从滦平盆地大北沟组、大店子组123块样品的古地磁数据分析,揭示了一组高温特征剩磁分量,在95%置信度下通过正倒转检验（B级）,说明这组高温分量很可能代表岩石形成时的原生剩磁,其特征剩磁方向为:Ds=5.3°,Is=50.2°,k=36.8,a₉₅=2.1,相应的极位置为λ_p=79.3°N,φ_p=272.1°E,dp=1.9°,dm=2.8°。通过与华北地块、华南地块、辽西等的古地磁极对比说明130Ma以来这些地块之间没有明显的纬向上的相对运动,可能已经拼贴为一整体,但却表现出比较明显的11.6±3.5°的逆时针的旋转运动。古流向的确定是恢复沉积过程和沉积物来源或剥蚀区的一个有效手段。通过滦平盆地三道沟剖面大北沟组、大店子组123块样品的磁化率各向异性测试,恢复了大北沟组、大店子组的古流向。大北沟组与大店子组之间发生的古流向变化暗示了早白垩世期间燕山褶断带发生了由于构造运动引起盆地的剥蚀源区的隆升变动。本文还探讨了冀北滦平盆地及邻区白垩纪各块体的旋转运动模式及其运动量。根据燕辽地区最新的地层学研究进展,将本区地层进一步划分为早白垩世中期、早白垩世晚期与晚白垩世三个阶段对该区古地磁数据进行了精细分析。通过与华北-华南地块相应时期的古地磁极对比,说明朝鲜半岛及辽东早白垩世中、晚期相对于稳定的华北-华南地块顺时针旋转约23°,晚白垩世以来没有明显的旋转运动。冀北-辽西地区则出现了小幅度的逆时针旋转运动。以上旋转运动与郯庐断裂的活动和松辽等盆地的扩张具有密切联系。更多还原

【Abstract】 The Yanshan fold-and-thrust belt, Located at the northern margin of the North China block, has often been referred to as the cradle of Chinese geologists and becomes famous due to its strong intraplate deformation in the Mesozoic and Cenozoic. From the beginning of the last century, many researchers have been focused on the Mesozoic stratigraphy and tectonics in this area and much progress was done and achieved. However, the correlation of the Mesozoic strata and the tectonic progress are still controversial, and more researches are needed to clarify these problems.The study of paleomagnetism has been developed for the Early Cretaceous strata at Luanping basin, eastern Yanshan fold-and-thrust belt. On the base of the new zircon SHRIMP U-Pb dating of the Dadianzi formation in the Luanping basin, the top of the Dadianzi formation was constrained to 131±6Ma. The Sandaogou section with Dabeigou, Dadianzi and Xiguayuan Formations at the Luanping basin, northern Hebei province, has a well-exposed and complete sedimentary sequence with rich fossils. Based on the magnetostratigraphic study at this section, a magnetic polarity sequence of the Dabeigou-Dadianzi Formation has been established. The integration of biostratigraphy, lithostratigraphy, chronosratigraphy and sequence-stratigraphy with high resolution magnetostratigraphic results suggest new ages of Dabeigou, Dadianzi and Xiguayuan Formations. It provides basic data for the stratigraphic classification and correlation of related strata in the northern Hebei province as well as China. The correlation between the magnetostratigraphic sequence of Sandaogou section and the MPTS indicates that the age of Aptian/Barremian boundary is 120 Ma, Barremian/Hauterivian is 125.1 Ma, Hauterivian/Valanginian is 130.4 Ma. The Dabeigou formation corresponds to the early of Valanginian, and the Dadianzi formation corresponds to the middle-late of Valanginian, and the lower part of Xiguayuan formation correspond to the Valanginian/Hauterivian.A stable magnetic component was isolated by stepwise thermal demagnetization of 123 samples from the Dabeigou and Dadianzi formations, which is characterized by a positive reversal test. A tilt-corrected mean direction is Ds=5.3°, Is=50.2°, k =36.8, a₉₅=2.1, corresponding to a paleopole atλ_p=79.3°N,φ_p=272.1°E, dp=1.9°, dm=2.8°. Comparisons of this paleomagnetic poles from the Luanping basin with those from western Liaoning, the North China Block （NCB）, the South China Block （SCB） and Eurasian plate imply that there were no relative latitudinal displacements and tectonic rotations between Luanping basin and western Liaoning, NCB, SCB, however, an anticlockwise rotations occurred between the Luanping basin, western Liaoning and NCB and SCB.The determination of paleocurrent directions is a robust approach to establish the sediments transport and of the deposition progress. A total of 123 samples from the Dabeigou and Dadianzi formations, the Sandaogou section at the Luanping basin have been measured, which provide Anisotropy of Magnetic Susceptibility data and paleocurrent directions information. The dramatic changes in paleocurrent directions between Dabeigou and Dadianzi formations imply that the slope direction change of Luanping basin resulted from the tectonic transfer of the Yanshan fold-and-thrust belt occurred at the early Cretaceous.In order to better understanding the block rotations between the Luanping basin and adjacent regions, we analyses mid-early Cretaceous, late-early Cretaceous and late Cretaceous paleomagnetic data respectively. The eastern Liaoning and Korean peninsula were rotated about 11°clockwise relative to the North and South China blocks between the mid-early Cretaceous and late-early Cretaceous. No significant rotations have been occurred since the late Cretaceous between Korean peninsula and the North and South China blocks. About 13°counterclockwise rotations of the northern Hebei-western Liaoning with respect to the North and South China blocks took place since the mid-early Cretaceous. These rotations are accommodated by the lithosphere thinning and extension beneath the Northeast China and adjacent regions, which resulted from the strong upwelling of asthenosphere caused by the subduction of the Pacific plate.更多还原