青藏高原东南缘兰坪—思茅地体晚始新世以来差异性地壳变形的成因讨论  

The contributing factor of differential crustal deformation of the Lanping-Simao terrane in the southeastern edge of the Xizang(Tibetan) Plateau since late Eocene

作　　者：杨向东 仝亚博[1,2] 王恒 裴军令[1,2] 孙欣欣[4] 王晨旭 杨振宇 YANG Xiangdong;TONG Yabo;WANG Heng;PEI Junling;SUN Xinxin;WANG Chenxu;YANG Zhenyu(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing,100081;Laboratory of Paleomagnetism and Tectonic Reconstruction,the Ministry of Land and Resources,Beijing,100081;Institute of Geology,China Earthquake Administration,Beijing,100029;College of Resources,Environment and Tourism,Capital Normal University,Beijing,100048)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]自然资源部古地磁与古构造重建重点实验室,北京100081 [3]中国地震局地质研究所,北京100029 [4]首都师范大学资源环境与旅游学院,北京100048

出　　处：《地质论评》2020年第4期853-873,共21页Geological Review

基　　金：国家自然科学基金资助项目“晚白垩世以来四川盆地旋转运动及其对盆地边界构造带新生代构造演化的控制作用”(编号:41872221);国家自然基金重大研究计划子课题“印度—亚洲碰撞过程拉萨地块和特提斯喜马拉雅地体的运动学研究”(编号:91855216);中国地质科学院基本科研业务费项目“特提斯消亡过程多陆块单向裂解—汇聚研究”(编号:JYYWF20182102)的成果。

摘　　要：印支地块北部地壳的侧向挤出逃逸方式和动力机制仍存在争议,本文通过兰坪盆地晚始新世红层的构造磁学和磁倾角偏低矫正研究,探讨了青藏高原东南缘大陆变形的成因等关键问题。磁倾角偏低矫正后的原生特征剩磁分量为Ds=264.5°,Is=-39.4°,k=21.4,α95=9.6°,N=12。结果表明自晚始新世以来,位于印支地块西北部的兰坪—思茅地体,其北部相对于东亚古地磁参考极发生了80.3°±8.9°的顺时针旋转运动,同时发生了5.8°±7.2°(638±792 km)的不显著南向运动。综合前人的古地磁研究结果,表明兰坪—思茅地体北部和中部地区存在显著的差异性旋转变形。本文提出地体北部~80°的顺时针旋转变形与印度板块东端和西缅甸地块向北揳入欧亚大陆联合作用造成的北东—东向挤压作用相关,而地体中部复杂的差异性旋转变形则与川滇地体的南向挤压和临沧花岗岩带的阻挡作用所导致的局部地壳构造变形相关。因此,兰坪—思茅地体北部和中部的差异性旋转运动是地体整体性顺时针旋转运动和局部差异性旋转变形相叠加的结果,与下地壳粘性通道流的驱动并无直接关联,而与相邻地块间的差异性运动所导致的地块间的挤压作用相关。自晚始新世以来,在兰坪—思茅地体北部地区上地壳沿大型走滑断裂带发生的东南向挤出逃逸运动和下地壳通道流所导致的上地壳韧性变形作用可能共存,而地体中南部地区沿大形走滑断裂带发生整体性侧向挤出逃逸模型可能占据主导地位。Objectives: The lateral extrusion model and dynamic process of the crust in the northern part of the Indochina block are still controversial. To solve this problem, this study applied tectonic magnetism and inclination-shallowing correction on the late Eocene red beds in the Lanping basin in the southeastern Tibetan Plateau in order to discuss these key issues of continental deformation in this region. Methods: According to the distribution of samples and the lithologic characteristics of samples, we selected three typical samples for rock magnetic experiments, and carried out stepwise thermal demagnetization experiments on the paleomagnetic specimens collected in Lanping area. Finally, we corrected the inclination by the 45° remanence anisotropy test.R esults: The directions of tilt corrected primary remanent magnetization was Ds= 264. 5°,Is=-39. 4°,k=21. 4,α95= 9. 6°,N= 12 after inclination-shallowing correction. These results showed that the northern part of the Lanping-Simao terrane experienced 80. 3°±8. 9° clockwise rotation and insignificant 5. 8°±7. 2°(638±792 km) southward displacement with reference to the paleomagnetic pole of East Asia since the late Eocene. Conclusions: Considering other paleomagnetic results of previous studies, it was clear that there were significantly different rotational deformations between the northern and central parts of the Lanping-Simao terrane. This study discussed the dynamic process of deformation of the Lanping-Simao terrane and suggested that the ~80° clockwise rotational deformation of the northern part of the terrane is related to NE-E trending compression caused by the northward wedging of both the eastern part of the India Plate and the West Myanmar Block into Eurasia, while the complex differently rotational deformation in the middle of this terrane was related to the regional crustal deformation caused by the southward compression of the Chuandian terrane and the obstruction of the Lincang granite belt. Therefore, the different rotation movement betw

关 键 词：青藏高原东南缘 兰坪—思茅地体 始新世 古地磁 侧向旋转挤出逃逸 磁倾角偏低 

分 类 号：P542[天文地球—构造地质学]