【作者】 张海峰；

【导师】 杨振宇；

【作者基本信息】 南京大学 ， 构造地质学， 2012， 硕士

【摘要】 思茅地区位于印度支那板块的北部,处在印度与欧亚碰撞的侧翼,是研究陆-陆碰撞过程中陆内变形作用的良好地区。本文在思茅地区对早白垩世碎屑岩开展详细的古地磁研究,以探讨陆内变形方式与过程,提高对欧亚大陆南缘地块构造变形的认识。思茅地区下白垩统曼岗组为陆源碎屑岩,以紫红色泥岩、粉砂岩和砂岩为主,布置镇沅、普洱和江城三个剖面,采集439块定向岩芯样品。岩石磁学实验(k-T曲线、等温剩磁和三轴等温剩磁)研究表明,样品中载磁矿物有针铁矿、磁铁矿和赤铁矿三种,以赤铁矿为主。热退磁结果显示大部分样品具有两个分量,少量样品为单分量和三分量,高温分量均为正极性,与白垩纪正向超静磁期相一致,镇沅、普洱剖面可通过褶皱检验,江城剖面为单斜地层,与前面两个一起可通过褶皱检验,说明高温分量是原生剩磁。三个剖面特征剩磁方向分别为镇沅：Ds=52.4°,Is=45.5°,κ=77.9,α95=6.3°,对应的古地磁极：42.9°N,175.9°E,A95=6.4°；普洱：Ds=46.2°,Is=46.6°,κ=50.9,α95=5.6°,对应的古地磁极：48.2°N,174.2°E,A95=5.8°;江城：Ds=8.6°,Is=42.2°,κ=117.1,α95=4.0°,对应的古地磁极：81.9°N,176.8°E,A95=3.9°。对普洱和江城剖面进行E-I磁倾角偏低检验,结果显示江城剖面不存在磁倾角偏低,普洱剖面由于偏角较分散,导致其伸展方向出现假象,推测的磁倾角偏大,出现实测磁倾角偏低的假象。思茅地区各采样剖面之间的磁偏角差异表明,块体内部发生过差异性旋转变形,其变形的过程不仅受控于边界深大断裂,也与内部小断裂的活动有密切关系。若进一步考虑华南地块白垩纪可能存在的磁倾角偏低现象,则该结果说明印度支那地块思茅地区白垩纪以来相对于华南地块向南滑移量为570±310km,接近构造地质研究推测的红河断裂带左行滑移量。更多还原

【Abstract】 Simao area is located in the northern part of the Indochina block, and in the flank zone of the Indian and Eurasian collision, where is the good area for the research to intracontinental deformation during continental collision. In this paper, paleomagnetic study was carried out on the Early Cretaceous clastic rocks at Simao area, aiming to explore the intracontinental deformation mechanism and processes, and to improve the understanding of structural deformation taken place in the southern margin of the Eurasia continent.At Simao area the lower Cretaceous Mangang formation are terrigenous clastic rocks, mainly red mudstone, siltstone and sandstone. A total of439oriented core samples were collected at Zhenyuan, Pu’er and Jiangcheng. Based on the studies of rock magnetism(k-T, IRM and triaxial IRM), have shown that goethite, magnetite and hematite are magnetic carrier minerals, and hematite is the main in samples. Thermal demagnetization results show that most of the samples exhibited two components, and a small amount of samples for the single-component and three-component.The high temperature components are all normal polarity, consistent with magnetization acquired during Cretaceous Long Normal Superchron. High temperature components from Zhenyun and Pu’er section can pass the fold test at95%confident level. Because of monoclinic strata in Jiangcheng section, combined the remanent direction with those from previous two sections also pass the fold test, these results idicate that the high temperature components are the primary remanence. The characteristic remanent magtization (ChRM) directions obtained from Zhenyuan, Pu’er and Jiangcheng area Ds=52.4°, Is=45.5°, κ=77.9, a95=6.3°, corresponding to a paleopole at42.9°N,175.9°E with A95=6.4°; Ds=46.2°,Is=46.6°, κ=50.9, a95=5.6°, corresponding to a paleopole at48.2°N,174.2°E with A95=5.8°; and Ds=8.6°, Is=42.2°, κ=117.1, a95=4.0°, corresponding to a paleopole at:81.9°N,176.8°E with A95=3.9°, respectively.The elongation/inclination (E/I) correction model was applied to evaluate the inclination error from the Pu’er and Jiangcheng sections.The results of the correction model indicate that inclination shallowing was negligible within the uncertainty in Jiangcheng, however there’s the illusion of inclination shallowing in Pu’er, as the declinations are scattered, resulting in the illusion of elongation in declination and the corrected inclination is apparent too large. The difference of declinations between all the sample sections at Simao area suggests that differential rotation has been taken place within the block, the deformation process is not only controlled by boundary faults, is also closely related with activities of the internal small faults. Taken a little shallow inclination in Cretaceous red beds in the South China block into consideration, the Simao area has been subjected to south displacement by570±310km with respect to the South China block since Cretaceous time, presumably close to the estimation of structural geology evidences.更多还原