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Poster Session Q
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Remote Sensing of active structure and geothermal in Tibet
An analysis of the active structures
Development of hydrothermal activity depends on three factors: 1}, thermal source, 2}, heat discharger conduit and heat-bearing reservoir, 3), water with heat energy. All of these are obviously in close relationship with geological structures.
Fig. 2 Active Structure Schematic Map in Tibet
According to this concept, we have interpreted some active structures, circular structures, principal graben valleys and basins and the uplift in whole Tibet, and draw up an interpretation map of linear and circular structures in Tibet and structural schematic map showing the prin-cipal structural zones. (Fig.2)
From the mosaic and the interpretation, the active structures can be divided into latitudinal, longitudinal and oblique zones. Each of the active structural zones is composed of linear structures, fracture structures, graben valleys, fault block uplift and magmation zones and some circular structures which are relate with the S-N compressive stress due to the subductin of the Indian plate down the Eurasian plate.
- Latitudinal Active Structural zone Latitudinal active structures are predominant ones in the area, and run parallel to the geosuture in space. They include the high Himalayan fault block uplifting zone, the Yarlung Zangbo structural zone, the Bangong-Nujiang structural zone and kunlun Kekexili structural zone. In addition, the secondary structures among them are pengqu fault depression zone, The Lower Watershed Uplifting Zone in South Tibet. Gangdise fault block uplifting region and subsidence region with many large lakes in North Tibet, from south to north.
Most of the structure zones near the Xiwalic thruat fault zone of the India plate are of new-born characteristics and are formed in the Himalayan Movement. For example, the high Himalayan fault block upkifting zone, the pengqu graben fault depression zone, etc. Northwardly, the structural zones are characterized by inheritance in the space. For example, the Yarlung Zongbo structural zone inherited the geosuture zone, which have been formed in late yanshan-Early Himalayan Period. Bengong-Nujiang structural zone inherited the geostructure zone, in Indo-China period. They occure as fault depression and uplift. There is a graben valley with a length of more than 500 km in the Bangong-Nujiang structural zone.
- Longitudinal Active Structural Zone
The S-N compressive stress combined with the mantle upwarping is responsible for 6 large longitudinal fracture zones, which are several hundreds km wide between each neighbouring zones[2].
Fig. 3 The image shows Shenza-Xietongmen longlitudial fault depression zone. It is obvious that graben valley always accompany fault black uplifts.
Langtutidinal active structural zone is characterized by its tensional forming graben valleys which extend to 10.20 km wide. This structural zone cut almost off all other oriented structural lines. In addition, this active structural zone is characterized by not only the flourishing longitudinal fault graben valleys but also the associated fault uplifts in the graben valleys as well as yarlung zangbo River Canyon in Nimu structural zone.
- Oblique Active Structural Zone.
They are mainly composed of NWW and NEE structural zones and secondarily, of NW and NE trending structural zones. They are characterized by sinistral or dextral equidistant trick-slip with an interval of about 150-200 km. The NWW trending structures are of great importance and may be devided into six structural zones from east to west, showing as fault depression, uplift, sinistral strike slip fault zone, long term active and trancriustal zones extending into the mantle[3]. For example, Anglaren Yangzhouyong structural zone, which lies in Central Tibet is up to 900 km long, in the central sector, it consists of a series of fracture zones, The eastern part of the zone is formed after the Yarlung Zangbo geosuture, cutting off the Yarlung Zangbo structural zone.
This structural zone is transcrustal structural zone extending into the lower crust and the mantle, it is demonstrated by the existence of Mohe mose upwarping on the mantle slope.
- Bomi Mssif
It is the most outstanding structure in East Tibet. It is about 800km long from Lancang River in the east to Nimu-Yang bajing in the west. We suggest that in the Early Yan shan Period the Gangdise structural zone was pregnant with the Bomi massif, which formed eventually in the Himalayan period.
The core of the massif is located at the turning point of the Yarlung zangbo River, in which the south Jiabawa Peak with elevation of 7756m, is the highest part in East Tibet. All the peaks have an elevation of more than 5500m, except for the Himalayan mountains which are located in the Bomi massif. During the Miocene Epoch, the Bomi massif obducted and napped the Chengdu structural basin.
- Circular Structures
Numerous circular structures in the area, for example, Naqu circular structures, Pengcuo circular structures etc. are active structures with the mantle upwarping and magmation.
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