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Poster Session Q
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Remote Sensing of active structure and geothermal in Tibet
He Yunzhong Liu Shangzhng Yuan Peixin
The Remote Sensing Station of the Sichuan Bureau of Geology and
Mineral Resources Chengdu, China
Tian Youhua Qinchang loug
The Geothermal-geological Team of the Tibet bureau of Geology and
Mineral Resources Lasa, China
Abstract
On the basis of the interpretation for the false color landsat MSS mosaic (1/500,000) of Mid-south Tibet with an area of more than one million Km2 we have found out different orientation and orders of active structural zones, and circular structures. Using the known hydrothermal active spots, we have discovered that hydrothermal activity is mainly located to the south of the latitudinal Banggong-Nujian structural zone, and the most located to the south of the latitudinal Banggong-Nujiang strcutrual zone, and the most intense is near the Yarlung Zangbo structural zone. The high-temperature hydrothermal spots are mainly distributed over these active structural zones of different orientations, such as the longitudinal fault depression zones, the NWW-NW trending fault depression zone, the NE trending fault depression zone and the latitudinal fault depression zone, the are-shaped margin of the Bomi massif and the arc-shaped fault depression zone in the margin of the circular structures.
We have finished the false color composite of 47 scenses MSS images with the I2 S 101 image system and made the processing mosaic by hand, so that we can investigate rich geothermal resources at a high-speed and coordinate regionalism study of geothermal resource in Tibet. The mosaic is at the scale of 1/500,000 which is 4.5 m long and 1.2m wide, and covers an area of more than one million Km2, which is characterized by its clearness and is good for geological interpretation (Fig.1)
For the sake of enhancing the useful information, we have performed various image processings for some important subareas. In addition, for some important hydrothermal area, we have used black-and-white aerial photographs for interpreting.
Indexes of geological interpretation of hydrothermal activity
We have got some interpretation key of hydrothermal spots by the interpretation of known spots and investigation in the field they are as follows:
- Sediment Index
Underground thermal water contains large amount of carbonate and a small amount of halides[1]. Reaching the surface, the thermal water discharges above-mentioned salts around hydrothermal sports and their neighborhood. These salt sediments are white.
- Vegetational Index
The hydrothermal areas are Long-term frostless, and even perennially ice-free, because of hydrothermal activities. Thanks to the condition above mentioned with hydrologic factors, the hydrothermal areas process a microclimate suitable to the growth of plants, thus the hydrothermal areas are covered perennially by green vegetation.
- Hydrothermal Alteration Index
Underground thermal water alternates the wallrocks, especially, feldspare-rich rocks such as granitoids. The resulted hydrothermal alteration zone especially when it contains a vast of kaolinite and sericite, may be used as an element of image interpretation too.
- In addition, perennially ice-free river and perennially snow-free sector can be used as an element of image interpretation
Fig.1 It is a sketch of the masaic map of Landsat MSS images in Middle South Tibet, the scale of 1:500,000, 4.5m long, 1.2m wide, and composed of 47 standard images. The semi-circular white image is Bomi mass if in the eastern masaic map.
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