长乐—南澳断裂带中生代活动特征及大地构造属性

Characters of the Mesozoic Tectonic Activity and Geotectonic Setting of the Changle-Nan'ao Fault Zone

长乐—南澳断裂带出露于闽粤沿海地区,断裂带中变质变形花岗质岩石分属晚侏罗世早期、晚侏罗世晚期、早白垩世早期等3个时期。不同期次侵入岩的变质变形特征、糜棱叶理的切割关系及锆石微区(LA-ICPMS)U-Pb同位素测年数据等,表明断裂带在中生代发生了3期韧性剪切变形及相关的动力变质作用:第一期为晚侏罗世(155～145Ma)低角闪岩相变质、深部构造层次长石相塑性变形;第二期为晚侏罗世末(145～137Ma)高绿片岩相变质、中深层次长石-石英相塑性变形;第三期为早白垩世早期(约120Ma)低绿片岩相变质、中—浅层次石英相韧-脆性变形。在3期变形中,断裂带运动特征不同:第一期为由北西西向南东东的右行-推覆韧性剪切变形,位移量约21km;第二期为由北北西向南南东的左行-逆冲韧性剪切变形,其位移量估计达84km;第三期为具正断层性质的右行走滑韧-脆性剪切变形(主剪切面倾向反转为倾向南东),位移量不足2km。长乐—南澳断裂带是一条中生代的大型陆内韧性剪切带。

Metamorphic and deformed granitic rocks in the Changle-Nan’ao fault zone,located in the coastal area of Fujian and Guangdong Province,was formed in the earlier Late Jurassic,later Late Jurassic and Early Cretaceous periods.It’s evidenced that three stages of ductile deformation and related dynamic metamorphism were developed within the fault zone during Mesozoic era,which are evidenced by metamorphism,deformation,crosscutting relation of the foliation and U-Pb isotopic dating of different intrusions.The first stage is characterized by deep structural level plastic deformation and low amphibolite facies metamorphism,which took place at the end of the Middle Jurassic（155-145 Ma）.The second,occurred in the Late Jurassic（145-137 Ma）,is characterized by the middle-deep structural level ductile shear deformation and high greenschist facies metamorphism.The third was demonstrated by mid-shallow brittle-ductile shear deformation and low greenschist facies metamorphism and formed in the middle period of the Early Cretaceous（about 120 Ma）.These shear deformations were dextral-thrusting from NWW to SEE（displacement about 21 km）,sinistral-thrusting from NNW to SSE（with the displacement of about 84 km）,and normal-dextral strike slip（displacement ca.2 km）,respectively.The Changle-Nan’ao fault zone is a continental intraplate giant ductile shear zone during the Mesozoic era.