庐山变质核杂岩东侧的伸展拆离及构造意义

庐山变质核杂岩东侧的星子牛屎墩地区出露与西侧拆离带相似的伸展拆离滑脱、韧性流变的构造现象, 岩层整体呈现上盘向南东滑脱的正断层性质, 推测庐山变质核杂岩东侧的拆离带就在此处, 而并非五里正断层。东侧拆离带内岩石以糜棱岩、糜棱状岩石及混合岩为主, 并发育大量的长英质脉体, 形成温压较高, 埋深较大, 其糜棱岩带、构造片岩带保留完好。运动学涡度分析得到涡度W_k>0.75, 表明该拆离系为以单剪为主的一般剪切带。根据糜棱岩中长石的变形特征估算东侧拆离带的形成温度为650 ℃~700 ℃, 与西侧拆离带近于一致。锆石U-Pb年龄测定得到东侧拆离带的伸展年龄为140~135 Ma, 也代表了庐山变质核杂岩的形成时间。

Extensional detachment structures in the east of Lushan metamorphic core complex

The extension-detachment and ductile rheology similar to the western detachment belt outcrop in Niushidun, Xingzi, east of Lushan metamorphic core complex. The hanging wall of rock stratum slipping to the southeast shows its normal faults' property. And it is speculated that the eastern detachment belt of Lushan metamorphic core complex is exposed at this region rather than Wuli normal fault. The rock of the eastern detachment belt mainly contains mylonite, mylonitic rocks and migmatite, it also develops a lot of felsic veins. The formation temperature and pressure is relatively high and the buried depth is relatively deep. The mylonite zone and tectonic schist zone are preserved well. Kinematic vorticity is greater than 0.75, shows the detachment belt is given priority to simple shear. The formation temperature of the eastern detachment belt is 650 ℃~700 ℃ according to feldspar's deformation characteristics in mylonite, and the result is consistent with the western detachment belt. The extension age of the eastern detachment belt tested by zircon U-Pb dating is 140~135 Ma, it also represents the formation time of Lushan metamorphic core complex.