| Summary: | 碩士 === 國立中央大學 === 地球科學學系 === 106 === Danba antiform, an area with extreme exhumation, locates between Longmenshan orogen and Xianshuihe sinistral fault zone in the eastern Tibetan Plateau. The Tibetan plateau was built by the convergence between Indo-Australian plate and Eurasian plate since early Cenozoic. However, the eastward lower crustal flow under the plateau obstructed by the Yangtze craton soon after this convergence and generated a very complex structural phenomenon. We used two methods, stress analysis and magnetic measurement, to understand the processes and mechanisms of this structural complexity. First, to be aware of the principle compressive stress in this area, we measured slickensides in the field from Danba area to Xianshuihe fault zone to carry out a series of analysis. We then obtained the strike of the maximum principle stress axis is NE-SW in Danba antiform, WNW－ESE in Xianshuihe sinistral fault zone, and no united trend on the peak of Zheduoshan. The possibility is the Gongashan granite which Zheduoshan located is a positive flower structure. Some of the principle stress are not horizontal or vertical here that made the stress trajectories diverse. In addition, in order to understand the magnetic characteristics of low-grade metamorphic rocks in this area, we took samples and processed the rock magnetic measurement of hysteresis loop. Then ensured the component of magnetic minerals by X-ray diffraction analysis (XRD) and Scanning Electron Microscope (SEM). The occurrence of pyrrhotite can be taken as an important isograd between anchizone and epizone in low-grade metamorphic rocks, which is helpful for stratigraphic and structural studies. Our study compared with the Triassic formation which appear both side of Xianshuihe sinistral fault zone, then observed pyrrhotite distributed between Xianshuihe sinistral fault zone and Danba antiform only. No any pyrrotite be found in the other Triassic formation. It means the Triassic formation in the northeast side of Xianshuihe sinistral fault zone is in epizone. The combination of our result shows there are fold-thrust zone and compressive strike-slip zone causing the uplift in the northeast side of Xianshuihe sinistral fault zone in a long period.
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