关键词: 糜棱岩, 剪切带, 正断层, 大别山

Abstract: The Yaohe pluton,found at the northeastern margin of the Dabie mountain recently,is a quartz diorite intrusive body. A precise ⁴⁰Ar/ ³⁹Ar hornblende dating age demonstrates that it had emplaecd in middle Jurassic (155.8Ma). The aluminum in hornblende geobarometer analysis indicates the crystallization pressure of this pluton is about (2.65±0.5)×10⁵Pa,and its emplaced depth is about 9km. Mylonite zone in the northern margin of the Yaohe pluton,those foliations dipping to NE direction,is the resultant of ductile shearing by the Mozitan Xiaotian fault. Macrostructures and micro ultramicrostructures in this ductile shear zone show the hanging wall of this normal fault moves down to NE direction,and the vertical difference uplift between two fault walls reaches to 9km. Combined with regional and deep structures,our study shows that eastern Diabie orogen does not possess“flowered”structure.

Key words: Mylonite, Shear zone, Normal fault, Dabie mountain