Identification of metamorphic rocks in Wuliangshan Mountains (Southwest China) using ASTER data

Metamorphic rocks have scientific significance for parsing the evolutionary process of an orogenic belt. The Wuliangshan area is a very complex region of metamorphism, where it is nearly impossible to conduct conventional geological investigation because of the extremely rugged topography and difficult travel conditions. Previous research on the area's metamorphic rocks is limited. There are two metamorphic belts, the Yunling-Jinghong and Wuliangshan metamorphic belts, identified by means of traditional field survey. To better identify the metamorphic rocks of the Wuliangshan area, this study adopted the principal component analysis (PCA) and spectrum-area (S-A) methods, using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data, to extract the anomalies of diagnostic metamorphic minerals in metamorphic rocks, such as actinolite, chlorite, epidote, biotite, muscovite, hornblende, andalusite, staurolite, cordierite, and sillimanite. The methods are based on the principle that the metamorphic degree is reflected by the diagnostic metamorphic minerals. Profile investigation and petrographic analysis show that the identification accuracy of the diagnostic metamorphic minerals reached 85.65%. Seven concentrations of metamorphic rocks were delineated based on the extracted metamorphic mineral anomalies. Compared with previous study results, this study showed that there are metamorphic rocks in defined Regions 1, 2, 3, 4 and 6, which are consistent with existing data; whereas in Regions 5 and 7, there is new information regarding the existence of metamorphic rocks, which may offer new clues about the formation of this area through additional studies. The results of this study not only reveal detailed information for geological survey of the Wuliangshan area but also provide useful methods for future surveys.