藏南拉轨岗日变质核杂岩带三层结构的影像证据及意义

Image evidence of the three-layer structure of the Lhagoi Kangri metamorphic core complex zone,south Tibet and its significance

拉轨岗日变质核杂岩带是喜马拉雅造山带的组成部分,从几何学角度查明其结构是该变质核杂岩带研究的一个重要内容。利用遥感技术来宏观地研究该变质核杂岩带的空间结构及物质组成,是对野外调研成果的有效验证和有益补充。从遥感图像信息提取的结果可以看出,变质核、过渡带及盖层在色调(色彩)、空间形态、水系类型与分布状况、影纹图案等各个方面均存在不同程度的差异。这些光谱及空间特征的综合使得变质核杂岩的三层结构被清晰地显现出来,尤其是过渡带的弱信息也在有TM6加入的K-L变换等图像处理手段中被有效地提取出来,从而更确切地证明该变质核杂岩带具有三层结构。同时,结合已有资料从遥感信息机理方面探讨三层结构各自的物质组成及其演变,为西部地区深入分析区域地质构造提供了一种有效的方法。

The Lhagoi Kangri metamorphic core complex zone is a component of the Himalayan orogenic belt. A thorough investigation of its structure, from a geometric view, is an important topic in the study of the metamorphic core complex zone. Macro-study of the structure and composition of the metamorphic core complex zone using remote sensing is an effective method and a valuable supplement to field investigation. Some methods were applied successfully to the image processing, such as K-L transform, ratio operation, tasseled cap transform, IHS transform, contrast enhancement and spatial enhancement. The effect of K-L transform, ratio operation and IHS transform is remarkable for extracting information of the three layers and composition of the metamorphic core complex zone. The image of the 3rd principal component from K-L transform concentration shows the spatial form of metamorphic core complexes. Especially, spatial profiles of transitional zones and cores and their dividing lines were distinctly displayed. On the pseudo-color composite images of PC3, PCA and PC5, transitional zones show a circular spatial entity with wine hue and without a micro-topographic texture. In the ratio operation, the standardization ratio can nicely extract layer-loop structure information from inner to outer portions of the metamorphic core complexes. The resultant images of IHS transform can present good visual effects, which profit from hue expanding and saturation strengthening. Thus, applying IHS transform after a series of image processing, such as K-L transform, ratio operation and tasseled cap transform, is a good means of information extraction. The information extracted from such images can distinctly distinguish the metamorphic core, the transitional zone, and the cover by their different characteristics of hue （color）, geometry, drainage system type and its distribution and texture patterns. Synthetically, these spectral and spatial image characteristics enable the three-layer structure of the metamorphic core complexes to be clearly seen. Particularly, the faint information of the transitional zone can be effectively extracted through the assistance of a series of image processing methods on the condition that TM6 is one of the participating（such as K-L transform, etc. ）. This paper confirms the three-layer structure of the Lhagoi Kangri metamorphic core complex zone, and discusses the composition of each complex layer and its evolution based on remote sensing techniques and considerable existing data. Some conclusions in this paper can be valuable for the regional tectonic analysis in this area in Tibet.