Deformation and metamorphic characteristics of amphiboles in the Luonan-Luanchuan fault belt of the Qinling Orogen and its significance

The deformation behavior and the component variation of amphiboles in the meta-mafic rocks in the fault belt are important means to study deformation environment and tectonic evolution of the fault belt. They also provide important information for study the rheological characteristics of amphibolites in mid-crust. With deformation and metamorphic analysis of amphiboles in the basic mylonite and the tectonic schist from Miaozi structural section of the Luonan-Luanchuan fault belt, it is suggested that the amphibole mainly deformed as BLG and SR, and the deformation environment should be amphibolite facies. Microprobe analysis indicated that all of the amphiboles are actinolite with significant compositional zoning. Al2O3-TiO2 graphic of amphibole shows its component most like to be mantle-crust mixing origin in the core and crust-source in the edge. (Na + K)-Ti variogram shows the formation environment of the amphibole is mainly amphibolite facies, and granulite facies in the core, greenschist facies in the edge. The feldspar intergrowth with amphibole also has significant compositional zoning, which are basic in the core and acidic in the edge and matrix. With feldspar amphibole experimental geothermobarometry, we figured up the temperature and pressure are respectively 620 similar to 640 degrees C and 0.4 similar to 0.7GPa in the core, 490 similar to 520 degrees C and 0.15 similar to 0.65GPa in the mantle, and 465 similar to 482 degrees C and 0.5 similar to 0.8GPa in the edge. In conclusion, the core of amphibole in the basic mylonite from Miaozi profile was formed in comparatively deep environment with higher temperature and the edge with crust-source compositional zoning was formed in the process of ductile deformation and retrograde metamorphism during shearing of the fault belt, which indicates the uplift during tectonic activities. So, metamorphic and deformation analysis of amphibole from fault belt can help reveal the tectonic activity process and the temperature-pressure environment, which has important significance to study the forming environment and evolution of fault belts in orogenic belt.