A study of the Yaohe pluton and its northern ductile shear zone at northeastern margin of the Dabie mountain

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) × 10 5Pa, 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.