为了探究鲜水河断裂带的几何学、运动学特征,在野外构造、显微构造分析基础上,研究了鲜水河断裂带296块构造岩定向样品的磁组构特征和热磁特征,结果显示样品的平均磁化率km值总体较小,属微弱磁性到弱磁性；热磁实验及其显微构造表明顺磁性的页硅酸盐(如黑云母)等矿物对糜棱岩类样品磁化率贡献较大；磁化率各向异性度PJ总体较大,表明鲜水河断裂带构造变形强烈；磁化率椭球体形状参数T总体大于0,扁率E总体在1附近分布,说明鲜水河断裂带磁化率椭球体以扁圆形为主,整体上磁面理较磁线理发育,进一步显示出鲜水河断裂带构造变形样式以剪切、压扁为主,伴有拉伸的构造变形,同时也反映出鲜水河断裂带多次变形的综合特征；最小磁化率主轴Kmin方位表明鲜水河断裂带北段和南段分别受近EW向和NE-SW向主压应力控制；同时Kmin方位及其倾伏角特征显示鲜水河断裂带总体以左行走滑剪切为主,北段两侧块体在鲜水河断裂带两次不同的构造活动时期,各自有一定的相对抬升,但抬升幅度均不大；南段则是SW块体相对NE块体抬升,抬升幅度较大；整个断裂带特征显示出鲜水河断裂带在向南发展逐渐转化为挤压构造,这可能与青藏高原物质的向东逃逸受阻以及鲜水河断裂带与龙门山断裂带在此交接的地质背景不无关系.%In order to probe into the geometry and kinematics of the Xianshuihe fault belt, this paper carried out a structuralrndeformation characteristics research to the Xianshuihe fault belt through the anisotropy of magnetic susceptibility ( AMS) and thermomagnetic analyses of 296 oriented samples on the basis of the field structural, and microstructural analyses. Average susceptibility ( km ) values of the collected samples are generally small so that they are slightly weak magnetic to weak magnetic. Thermomagnetic curves and microstructure demonstrate that paramagnetic minerals such as biotite might be the dominant contributions to the susceptibility of the mylonite ones. Anisotropy degrees of the magnetic susceptibility ( PJ ) are relatively large indicative of a strong structural deformation of the Xianshuihe fault belt Shape parameter (T) are generally more than zero and the flattening ( E) distribute around 1, indicating that the susceptibility ellipsoid of the Xianshuihe fault belt is mainly oblate. Compared to the magnetic lineations, magnetic foliations are relatively developed, demonstrating that the main deformation styles of the Xianshuihe fault belt are shear and flatten with stretch. This further indicates that the Xianshuihe fault belt has comprehensive features of multiple structural deformations. Orientation of minimum susceptibility principal axis (Kmin) showed that the northern and southern section of Xianshuihe fault belt were controlled by nearly EW and NE-SW compressive stress. On the other hand, the Kmin orientation and its plunge angle characteristics showed that the Xianshuihe fault belt was mainly characterized by left-lateral strike-slip shear and the blocks on either side of the northern section had a certain relative uplift respectively in two different tectonic movement stages although lifting amplitude were small. In the southern section, SW block lifted, compared with the NE side. The whole characteristics of Xianshuihe fault showed that it is evolving southward gradually transforming into a compressive tectonic. It might be related to the tectonic setting what eastward escape of materials of the Tibetan Plateau and connection of Xianshuihe fault with Longmenshan fault belt.
展开▼
