胶南地区的伸展作用——以胶南—诸城一带为例

胶南地区的胶南—诸城一带存在两期不同方向的伸展构造。早期以形成近ＥＮ向的拉伸线理为特征，并在不同构造层次上显示出不同的变形。出露于研究区中部桃林尚庄隆起的含榴辉岩片麻岩中，主要以ＬＳ的组构为特征，显示出早期伸展作用下地壳岩石的垂直轴缩短、ＥＷ向拉伸的共轴应变；而在把下地壳含榴辉岩片麻岩与以变沉积岩为主的中上地壳岩石分开的韧性滑脱带上，此期伸展作用则表现为从东向西剪切的非共轴简单剪切变形，具有近水平的拉伸线理及近水平的ＥＷ向剪切褶皱和鞘褶皱枢纽。晚期伸展作用表现为近ＳＮ的伸展垮塌作用，形成向北和向南倾斜的两条韧性正剪切带，且遭受低角闪岩高绿片岩相条件下的透入性均匀简单剪切变形，剪切方向分别向北和向南。

Extension of Jiaonan Area in Shandong

Jiaonan area experienced two period different direction extension. The early extension is characterized by subhorizontal E W stretching lineations and displays different deformation in different levels. The eclogite bearing lower crust gniesses, which cropout in the centre part of studies area, show LS constrictional strain fabrics with subhorizontal or gently W plunging lineations under eclogite facies metamorphism. These fabrics indicate that eclogite bearing lower crust experienced vertical flatting, subhorizontal stretching and S N compression. The detachment zone, which separated middle upper crust meta sedimentary rocks from lower crust eclogite bearing gniesses, suffered homogeneous simple shear from east to west under amphibolite facies condition with subhorizontal E W stretching lineations and hinges of shear folds and sheath folds. The late extension is characterized by S N extensional collapse. The subhorizontal detachment zone was rotated into E W striking, N dipping and S dipping ductile extensional shear zones with width of several hundred metres to several kilometres. The stretching lineations plunge separately toword NNW NNE and SSE SSW and overprinted on the early subhorizontal E W stretching lineations. Deformation structures and mineralogical petrological studies indicate that two ductile extensional shear zones underwent separately top to the north and top to the south penetrative homogenous simple shear under high greenschist facies condition.