Abstract:

The Liaonan metamorphic core complex (MCC) developed a NNE trend, NWW-dipped, low-angle detachment fault. Ductile shear zone occurred in the lower part and mainly consists of mylonitic granitic gneisses, which indicated a top-to-NWW shearing. Finite strain measurement of feldspar strain markers were estimated by the R_f /φ method. It suggested that strain intensities of mylonites (E_s) changed from 0.36 to 1.0 with an average of 0.75. Fulin and Hossack diagrams indicated strain types were close to flattening strain (lod parameter υ=0.11-0.98). Kinematic vorticity of mylonitic foliations and stretching lineations were estimated by Mohr diagram method and long and short axis method. The results indicated that kinematic vorticity ranged from 0.74 to 0.96 with an average of 0.85, which suggested that the foliations and lineations of mylonites recorded a bulk simple-dominated general shearing. The Kinematic vorticity during formation of extensional crenulation cleavage estimated by C′ method ranged from 0.10 to 0.84 with 0.58 on average. It recorded a later bulk pure-dominated general shearing. Based on the strain measurement, kinematic vorticity and thickness of the detachment fault, the quantification of thinning for the ductile shearing were calculated, which ranged from 130 to 705 m. All results suggested that the deformation mechanism of the Liaonan MCC was represented by earlier simple-dominated shearing and later pure-dominated shearing.

Key words: strain, kinematic vorticity, ductile thinning, metamorphic core complex, ductile detachment zone, mylonite, extensional crenulation cleavage

摘要：

辽南变质核杂岩西侧为一NNE 走向、NWW 倾向的低角度拆离断层带, 其中韧性剪切带由位于拆离断层带下部的糜棱岩组成, 糜棱岩中所有运动学指向标志都指示上盘向NWW 方向的伸展拆离。基于长石的R_f /φ 有限应变法, 对该糜棱岩进行测量, 结果显示糜棱岩的应变强度(E_s)介于0.36~1.0 之间, 平均0.75。付林图解与霍塞克图解显示应变类型为压扁型(罗德参数υ=0.11~0.98)。使用极摩尔圆法与有限应变法测量糜棱岩面理与线理形成时的运动学涡度, 其值介于0.74~0.96 之间, 平均0.85。使用C′法获得的伸展褶劈理C′形成时的运动学涡度介于0.10~0.84 之间, 平均0.58。依据运动学涡度、有限应变及拆离带的真实厚度, 计算获得拆离带的韧性减薄量为130~705 m。综合以上结论, 辽南变质核杂岩剪切变形机制是以糜棱岩面理与线理发育为代表的早期单剪为主的一般剪切以及以伸展褶劈理发育为代表的晚期纯剪为主的一般剪切。

关键词: 应变, 运动学涡度, 韧性减薄量, 变质核杂岩, 韧性拆离带, 糜棱岩, 伸展褶劈理