北大别造山后穹隆构造的形成过程与变形模拟

Formation processes and deformation modeling for post-orogenic dome structures of the North Dabie

北大别穹隆是在早白垩世造山后伸展活动中形成的。其北界为北西西走向、倾向北北东、正左行平移的晓天—磨子潭韧性剪切带,南界为北西走向、倾向南东、右行"逆冲"的五河—水吼韧性剪切带。通过对这两条剪切带的构造观测、运动学分析、石英C轴组构测量、变形温度分析及变形模拟,表明剪切带原先为中地壳同一近水平的韧性拆离剪切带。该拆离剪切带在原始近水平状态时的活动为上盘向280°方位的伸展运动。随后在大规模岩浆活动与北大别穹隆的隆升中,这一剪切带被动地抬升与剥露,而出露于现今的穹隆边界上。变形模拟显示,北大别穹隆构造现今为近EW轴向的背形,其上隆幅度西强东弱。北大别穹隆的形成过程表明为典型的造山带变质核杂岩。

The North Dabie dome resulted from the post-orogenic extension in Early Cretaceous. The NWW- striking, NNE-dipping Xiaotian-Mozitan shear zone in the northern boundary of the dome is a normal sinistral, ductile shear zone whereas the NW-striking, SE-dipping Wuhe-Shuihou shear zone in the southern boundary is a dextral reverse, ductile shear zone. Field structural investigation, analyses of quartz C-axis fabric, kinematics and deformation temperatures as well as deformation modeling for the two shear zones demonstrate that they originated from the same subhorizontal, mid-crust-level ductile shear zone with shear sense of top-to- NWW（280°） and dominance of simple shear deformation. Thereafter, this subhorizontal shear zone outcropped at the boundaries of the dome due to exhumation related to doming of the North Dabie associated with massive magmatism in the Early Cretaceous. Deformation modeling indicates that the present North Dabie dome occurs as an anti{orm with an E-W trending axis, and the western segment of the dome experienced more intensely doming than the eastern. It can be concluded from the development that the so-called North Dabie dome belongs to typical metamorphic core complex in the Dabie orogenic belt.