基于ASTER光谱特征的科技廊带岩性填图:以新疆塔什库尔干地区为例

Scientific belt lithologic mapping based on ASTER spectral analysis:A case study from the Tashkorgan area(Xinjiang,China)

科技廊带填图是以解决关键地质问题为目的填图方式,但部分地区海拔高差大,交通不便,给填图工作造成巨大困难。遥感岩性解译可为填图工作提供重要参考。然而,当前主流的遥感岩性解译方法仍是基于地貌纹理等间接解译标志开展的。相对而言,矿物岩石光谱特征作为最为直接和准确的遥感岩性解译标志却少有实例报道。本文基于ASTER遥感影像和岩石光谱特征分析,对部分地区海拔高差较大的新疆塔什库尔干地区进行岩性解译工作,以检验其适用性。在野外工作对研究区岩性类型进行识别和鉴定的基础上,ASTER光谱分析成果影像可较准确显示区内主要岩性类型的地表出露。其中,ASTER热红外波段比可反映区内中高级变质岩、花岗岩类及碳酸盐岩的整体分布特征;在此基础上,ASTER可见光-近红外及短波红外波段比可准确鉴定与Fe^(3+)、Fe^(2+)-硅酸盐、Al-OH、Mg-OH等成分相关的矿物组成(如绿泥石、白云母及石榴子石等),从而对地表岩性出露进行更为细致的识别和分类。研究结果表明基于ASTER光谱特征的岩性填图方法在新疆、西藏等地区有天然的实用性,既可克服区内海拔高、交通不便等困难,又可准确指示地表关键岩性类型的出露情况,可作为科技廊带填图及地质研究工作的重要手段。

Scientific belt mapping is based on the key geological question for the mapping area. However, some of the mapping areas are not easy to reach because of the high altitude, and lithologic mapping based on remote sensing image can provide useful information for the mapping project. Advanced Spaceborne Thermal Emission and Reflection （ASTER） remote-sensing data are useful in assisting lithologic mapping and, however, it has been rarely applied by in the Xinjiang and Tibetan areas and its effectiveness in these areas needs to be verified. In this paper, based on combined field geology and ASTER data analysis, we present mapping methodology and results from the Tashkorgan area of western Xinjiang. The Tashkorgan area is a key area for studying the Himalayan- Tibetan orogen and the Tethyan ocean evolution. Nonetheless, the high altitude and poor transportation conditions of this area have imposed major difficulties on geological mapping. Lithologic types of the Tashkorgan area mainly include intermediate-high grade metamorphic rocks, Paleozoic （Ordovician, Silurian, Upper Carboniferous and Permian） meta-sedimentary rocks and various types of intrusive rocks. ASTER spectral analysis is shown to be effective identifying and discriminating the lithologic types. In particular, the ASTER TIR bands were processed first to reveal distribution of prominent lithologic types, including quartzose rock, quartz-deficient rock and carbonate and establish references for followed lithologic matching. The VNIR/SWIR band ratio indexes were demonstrated to effectively highlight spectral features related to lithologic composition of Fe3 ＋, Fe-silicate, A1-OH, Mg-OH and carbonate. The lithologic mapping results provide more refined lithologic information than the previous map, which demonstrates the effectiveness of this method. The generalized procedures of ASTER-assisted lithologic mapping are applicable for future geologic mapping projects and studies in the similar areas such as Xinjiang and Tibet.