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

摘要： 位于东大别山北缘的姚河岩体是最近确定的中侏罗世石英二长岩体,角闪石⁴⁰Ar ³⁹Ar法定年为155.8Ma,用角闪石压力计法得出结晶压力为(2.65±0.5)×10²MPa,结晶定位深度约9km。岩体北缘发育的NE倾的糜棱岩带是磨子潭 晓天断裂韧性剪切的结果。对剪切带中宏观标志及显微、超显微构造研究表明,该断裂自中侏罗世之后主要表现为上盘向NE方向下滑的正断层,两盘垂直差异隆升达9km。结合区域构造及深部资料分析显示,东大别造山带并不具有“翻花状”双侧造山链特点。

关键词: 糜棱岩, 剪切带, 正断层, 大别山