Abstract: The research tries to solve the problem of lithological classification in the area where it's hard to implement a geological survey, in the meanwhile, by using a thermal method to find tectonic features which are hidden under the visible light. Some minerals, like quartz and feldspar, do not exhibit absorption features in the VNIR and SWIR regions, but display fundamental molecular absorption features in the TIR wavelength region.These characteristic spectra always reserve on the rock surface's measured spectra. On the basis of the emissivity spectra of the rock samples which are measured by FTIR in the region of thermal infrared spectroscopy, the lithology could be classified by band ratio method of ASTER TIR image. The measured emissive spectra of blueschist rock samples' in Akesu carry a large amount of information. The Restrahlen Features (RF) positions of muscovite quartz schist are similar to that of the monzonitic quartz schist. Their resampled spectra curve shows that the rock emissivity increases from ASTER Band 12 to Band 13, but only muscovite quartz schist has a higher emissivity value in Band 13 and Band 14 than Band 10 and Band 12, which could be distinguished from other samples. The Muscovite Index (I_m=((B14·B13)/(B10·B12)) is established to indicate the distribution of muscovite's content in the study area. The chlorite epidote schist's spectra are in the high value position, which is the same as that of the rock diabase, but it still has a significant RF position in wavelength 10.5μm corresponding to the ASTER Band 13. So we built up the Basite Index (I_b=(B12·B14)/(B13·B13) to indicate the basic rocks in Akesu geological body. According to these two expressions, we obtained band ratios on ASTER TIR emissivity products, and got the results of Akesu thermal infrared I_m and I_b image in a colored lookup table.
I_b and I_m images have a good reflection of the lithology distribution, which indicates a rich content of muscovite in the southeast Akesu and a rich basic rock in the northeast Akesu. The stratum in the northwest could be devided into several layers corresponding to the samples we collected in the field work. The diabases are clearly visible in I_b image. On the basis of these images, we drew a new Geological sketch map and found a rootless hook fold in Akesu blueschist. The previous research did not exhibit it on their map. The rootless hook fold indicates that the south part of Akesu blueschist bore a greater pressure than the north part. It illustrates a tectonic model of oceanic plate southward subduction to Tarim craton which has been put forward by Nakajima in 1990, and the thesis of Wentao Huang has a same conclusion as ours.
The authors consider that thermal infrared remote sensing has a wide application prospection for mineral identification and lithological classification.

Key words: measured spectra, ASTER TIR, mineral index, lithological classification, fold, blueschist