医巫闾山变质核杂岩南段韧性变形与流变特征

Ductile deformation and rock rheological characteristics from southern Yiwulüshan metamorphic core complex

医巫闾山变质核杂岩南段张家堡地区出露两套花岗质岩石：太古代花岗质片麻岩,含有黑云斜长片麻岩包体,以及晚期侵位钾长花岗片麻岩与花岗岩脉。详细宏微观构造分析发现,花岗质岩石遭受了两期变形事件：晚侏罗世高温韧性剪切和早白垩世低温韧性剪切变形。早期韧性变形温度约550-600℃,高绿片岩相-低角闪岩相,此次韧性变形以单剪作用为主,岩石为L=S和LS构造岩,具有右行剪切特征。晚期韧性变形温度约400-450℃,绿片岩相,变形以纯剪切为主的一般剪切,岩石以L=S构造岩为主,具有左行剪切特征。利用动态重结晶及亚颗粒粒径估算岩石流变学参数,结果表明高温剪切带具有较低差异应力,较高应变速率,低温剪切带恰好相反。早期晚侏罗世韧性伸展变形与伊泽那崎板块和法拉隆板块NNW向俯冲共同作用于欧亚大陆东缘相关,进入早白垩世伊泽纳崎板块向欧亚大陆俯冲深部板块后撤（Roll-back）,导致华北岩石圈发生大规模减薄,医巫闾山地区发生晚期低温韧性伸展变形。

The southern Yiwultuhan metamorphic core complex in Zhangjiabao area represents two suits of granitic rocks： Archean granitic gneiss which contains abundant biotite plagioclase gneiss enclaves; late intrusive K-feldspar granitic gneiss and granitic dykes. Detailed macroscopic and microscopic structural investigations indicate two ductile deformation events which developed in these granitic rocks： Late Jurassic ductile shear zone under high deformation temperature of about 550 - 600℃, and Early Cretaceous ductile sheafing under low deformation temperature about 400 - 450℃. Early deformation event was mainly formed under the condition of upper greensehist to lower amphibolite facies, which in simple dominated sheafing with L = S and LS tectonites with dextral sheafing characteristics. Late ductile deformation event was formed under greenschist facies metamorphism, consisting mainly of equally simple and pure sheafing with L = S teetonites with sinistral sheafing features. The estimation of rock theological parameters from dynamically reerystallized grain sizes of quartz indicates that early high temperature shear zone have a lower paleo-stress with higher strain rates, and opposite features exist in late lower temperature sheafing. Late Jurassic extensional deformation might be related to Izanagi Plate and Farallon Plate NNW obliquely subducting under the eastern margin of Eurasia plate. The late deformation event, occurred in Early Cretaceous, which is related to the lithospheric thinning and extension of the North China Craton triggered by roll-back of the Izanagi Plate beneath the eastern North China Craton.