辽西医巫闾山变质核杂岩的形成过程与晚侏罗世伸展事件

Evolution of the Yiwulüshan Metamorphic Core Complex and Late Jurassic Extensional Event in the Western Liaoning Province

根据野外详细调查,本文系统分析了医巫闾山地区的伸展构造,认为区内瓦子峪伸展韧性剪切带发育之前就出现了变质核杂岩。该核杂岩具有典型的三层结构,其拆离韧性剪切带出现在变质基底内,但西侧被晚期早白垩世瓦子峪韧性剪切带切割,呈不完整的长环形带状展布。露头构造、显微构造及石英C组构皆指示核杂岩的下盘、拆离韧性剪切带及上盘底部具有一致的上盘向SSW的运动学指向。拆离剪切带和下盘中同构造侵入了大量浅色花岗岩脉,其锆石LA-ICP-MS定年结果指示核杂岩形成于157～147Ma,表明研究区的伸展活动开始于晚侏罗世。医巫闾山晚侏罗世变质核杂岩的厘定,暗示燕山构造带上广泛出现的晚侏罗世岩浆活动应发生在区域性伸展背景下,华北克拉通北部可能从晚侏罗世已经开始发生破坏,到早白垩世达峰期并遍及整个华北克拉通东部。

Based on detailed field investigation,this paper systematically analyzed the extensional tectonics in the YiwulüMountain area,western Liaoning,and found that the Yiwulüshan metamorphic core complex（mcc）had developed before Waziyu ductile shear zone formed.It has a three-layer structure with an incompletely annular detachment ductile shear zone,which mostly occurred in the basement metamorphic rocks and was truncated by later Waziyu shear zone in the west.Analysis of the mesostructures,microstructures and quartz C-axis fabrics indicates that lower plate,detachment shear zone and the bottom of the upper plate has uniform top-to-the-SSW shear sense.LA-ICP-MS zircon U-Pb dating results of the syn-kinematic leucogranitic dikes from the detachment shear zone and its lower plate show that the Yiwulüshan mcc formed between 157 Ma and 147 Ma,suggesting that the area was under an extensional regime during the Late Jurassic.The revision of the Yiwulüshan mcc indicates that synchronous widespread magmatism in the Yanshan structural belt was under a regionally extensional regime,which implies the northern part of the North China Craton might destructed from Late Jurassic and reached peak period in Cretaceous throughout the whole eastern North China Craton.