Magnetic fabric study and its tectonic significance of suture zones in joint area of Qinling and Qilianshan
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摘要: 结合构造及磁化率各向异性研究详细解剖了秦祁接合带唐藏—关子镇—武山和新阳—元龙造山缝合带的应变及岩组特征.41个采点168个构造岩样品的平均磁化率全部较低，磁化率椭球形态分析表明其以平面和压扁应变为主，磁化率各向异性度普遍较高，属强变形岩石组构类型，结合野外观察认为其与变形强度明显正相关.此外，磁化率各向异性参数T、P′可能受岩石类型一定程度的影响.磁化率椭球主轴方位与变形密切相关，提供了丰富的岩组信息.两构造带具有类似的岩组特征，磁面理大致分为呈共轭形态的两组，暗示高应变剪切带在平面上可能以网格状形态出露；高倾伏角磁面理与占优势的低倾伏角、近水平磁线理表明了构造带明显的走滑特征，部分高角度磁线理可能与构造带的挤压和（或）转换挤压相关；磁组方法不能简单用于判别复杂强变形带的运动指向，糜棱面理的复杂变化及Kmin与构造带夹角过高使其判别结果意义不明，而野外及显微构造观察都表明了构造带的右行走滑特征.上述结果表明，沿缝合带大规模的右行转换挤压形成了秦祁接合带反“S”型的平面构造形态，暗示在南北板块拼合过程中，西秦岭诸中、小块体一定程度的向西挤逸.Abstract: Tangzang-Guanzizhen-Wushan and Xinyang-Yuanlong tectonic zones are the major suture zones in joint area of Qinling and Qilianshan mountains. Structure analysis and the anisotropy of low-field magnetic susceptibility (AMS) of 168 samples from 41 sites was measured to determine the strain and fabric of the high strain shear zone in the suture zones. Most of the mean susceptibilities (Km) are low. Magnetic ellipsoid analysis displays that most of the samples are dominated by shear and oblate compressional fabric, and have high values of anisotropy magnitude which increases with the intensity of deformation. Caution should be exercised when use T and P′ to deduce the shape of magnetic ellipsoid and the deformation intensity for they are also affected by rock types. The directions of principle susceptibilities are closely related to deformation, the magnetic foliations defined by Kmax and Kint are divided into two conjugate groups that imply the gridding configuration of high strain shear zone; clustered foliation and more scattered lineation are attributed to the shearing and flattening regime. Most of the samples have steep magnetic foliations and subhorizontal magnetic lineations and others have steep lineation, which demonstrate the transpressional characteristics of the shear zone. And shear sense of complex high strain zone inferred from magnetic fabric may be unreliable or even wrong for variation of the foliation attitude across the shear zone and great angle between Kmin and the striking of shear zone.
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