黄河源地区磁组构特征及其地质意义

黄河源区位于青藏高原东北部,区内主要为三叠系沉积地层,发育一系列由北向南的推覆构造带,间有早期近直立的韧性剪切带。笔者对黄河源地区巴颜喀拉山群沉积岩进行了磁组构分析,结果显示岩石磁化率各向异性度P值和磁化率百分率各向异性度H值均不大,反映该地区总体韧性变形较弱,较强韧性变形仅发育于局部地段;岩石磁组构具有磁面理发育、磁线理不发育、磁化率椭球呈压扁形椭球体的特点,反映在挤压应力作用下,岩石发生了压扁变形,主应力方位主要为NNE-SSW(近SN)向,其次为NE-SW向。根据岩石磁组构分析认为黄河源地区存在两条韧性剪切带,韧性剪切带与现今湖泊水体的展布有一定的耦合关系;北部韧性剪切带沿现今黄河河谷分布,控制着扎陵湖、鄂陵湖和玛多"四姐妹湖"的展布;南部韧性剪切带沿岗纳格玛错—野牛沟一线展布,控制着岗纳格玛错和尕拉拉错等残余湖泊的分布。

Magnetic fabric of rock in the source area of the Yellow River and its geological significance

The source area of the Yellow River located in northeast Tibetan Plateau is composed mainly of Triassic sedimentary strata.From north to south,a series of nappe structures and some early nearly-vertical ductile shear zones are developed.This paper presents the magnetic fabric of Bayankala Group sedimentary rocks in the Yellow River source area.It is shown that the rock magnetic susceptibility anisotropy(P value)and the percentage of anisotropy of magnetic susceptibility(H value)are not large either,suggesting overall weak ductile deformation in the area and strong ductile deformation in some parts.The magnetic fabric of rock is characterized by development of magnetic foliation,underdevelopment of magnetic lineation and flattened magnetic susceptibility ellipsoid,implying that rock endured flattening deformation in the compressive stress.The major principal stress is in NNE-SSW(near SN) derection,followed by NE-SW direction.Based on an analysis of rock magnetic fabric,the authors found that there are two ductile shear zones in the source area of the Yellow River.The ductile shear zones and the current distribution of lakes have certain coupling relationship.The northern ductile shear zone along the present Yellow River valley dominates the distribution of Zhalinghu,Elinghu and "Four Sister Lakes " in Maduo.The southern ductile shear zone along Gangnagema Co-Yeniugou belt controls the distribution of remnant lakes.