青藏高原东南缘兰坪-思茅盆地反S型构造属性的古地磁约束  

Paleomagnetic Constrains on the Reversed S-shaped Structure Deformation of the Lanping—Simao Basin in the Southeastern Xizang (Tibet) Plateau

作　　者：徐颖超[1] 仝亚博[1,2] 王恒[1] 杨振宇[3] 

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

出　　处：《地质论评》2017年第3期549-567,共19页Geological Review

基　　金：国家自然科学基金资助项目(编号:41572183);中国地质调查项目(编号:DD20160268,12120114002301);中国地质科学院基本科研业务费(编号:YYWF201613)的成果~~

摘　　要：兰坪—思茅(盆地)内部发育的一系列褶皱和逆冲断层组成了显著的弧形构造,其中部呈现反S形构造形态。该地区地壳构造变形方式及其演化过程与青藏高原东南缘地壳物质新生代侧向挤出逃逸密切相关,对其开展地壳构造变形方式的定量分析,具有重要的意义。本文通过兰坪—思茅盆地中部反S形构造区域四条白垩纪红层剖面的岩石磁学和古地磁学研究,获得南涧牛街地区早白垩世LN-a和LN-b剖面的特征剩磁方向分别为D_s=244.7°,I_s=-47.3°,Ks=31.6,α_(95)=16.6°(K_1j^1),和D_s=245.4°,I_s=-46.4°,K_s=52.2,α_(95)=9.4°(K_1n^2),两剖面在99%置信度下通过了Mc Fadden(1990)褶皱检验;小湾镇地区早白垩世NX-a和NX-b剖面(两套地层分属轴向不同的两褶皱)特征剩磁方向分别为D_s=244.9°,I_s=-40.2°,K_s=1067.5,α_(95)=2.3°(K_1j^1)和D_s=182.6°,I_s=-42.1°,K_s=335.2,α_(95)=3.7°(K_1j^2)。结合前人在兰坪—思茅地体中部获得的可靠古地磁数据及青藏高原东南缘区域新生代断裂活动演化过程的分析,指出兰坪—思茅盆地中部弧形反S形构造的形成和演化,以及兰坪—思茅盆地构造区内部差异性旋转变形作用主要受控于新生代时期青藏高原东南缘地壳块体侧向旋转挤出过程中的相互挤压作用和临沧花岗岩基对兰坪—思茅地体侧向顺时针旋转挤出运动的阻挡等一系列构造因素。Objective： A series of folds and thrust faults was formed in the central part of Lanping--Simao Basin that constituted of a reversed S-shaped structure. The quantitative analysis on the way and process of the Lanping-- Simao crust evolution has an important geological implication, because the crustal surface deformation and tectonic evolution are closely related to the tectonic evolution of the southeastern Tibetan Plateau. Based on paleomagnetic studies of the Early Cretaceous red beds and the tectonic evolution process of regional active faults in the Lanping-- Simao basin, the paper discusses the originated model of the reversed S-shaped structure in the central Lanping-- Simao Terrane. Methods： There are 211 representative paleomagnetic samples picked out from the Early Cretaceous red beds at four sections in Nanjian area of the central part of the Lanping--Simao basin, and then the rock magnetic and paleomagnetic studies were carried out. Results： The characteristic remnant magnetization （ChRM） directions obtained from two sections at Niujie area are Ds = 244.7°,Is = -47.3°,Ks = 31.6,α95 = 16.6 （K1j1） in the LN-a section, and Ds = 245.4°,Is = -46.4°,Ks = 52.2,α95 = 9.4 （K1n2） in the LN-b section, respectively. A fold test was performed on the two sections and was positive at the 99% confidence level （McFadden, 1990）. The tilt corrected site--mean directions from two sections at the Xiaowanzhen area are D8 = 244.9° ,Is = -40.2° ,Ks = 1067.5 ,α95 = 2.3 （K1j1） in the NX-a section, and Ds = 182.6°, Is = -42.1°, Ks = 335.2, α95 = 3.7 （K1j2） in the NX-b section, where the two sections are located in different limbs of the folds. Conclusion： We propose the originated model of the reversed S-shaped structure in the central Lanping-- Simao Terrane, showing that the formation, its evolution and differential rotations of reversed S-shaped structure were controlled by the extrusion effect of different small crustal blocks in the southeastern Tibetan Plateau during the India/

关 键 词：白垩纪 古地磁 兰坪-思茅盆地 反S形构造成因 旋转变形 

分 类 号：P318.44[天文地球—固体地球物理学] P542[天文地球—地球物理学]