鞍山地区太古宙地壳的构造演化序列

    THE TECTONIC EVOLUTIONARY SUCCESSION OF THE ARCHEANC CRUST IN THE ANSHAN AREA

    • 摘要: 鞍山地区的太古宙变质岩,主要由花岗质岩石(约占90%)和表壳岩(含铁岩系)组成。其中花岗岩包括铁架山花岗岩和弓长岭花岗岩,表壳岩由磁铁石英岩和绢云绿泥石石英片岩组成。表壳岩沉积年龄大于3000Ma,铁架山花岗岩侵位于2900Ma,稍后即发生第一幕韧性变形,在铁架山花岗岩中发育了NE走向片麻理,在表壳岩中形成同斜褶皱及轴面片理S_1。2600Ma左右弓长岭花岗岩侵位,稍后又发生第二幕韧性变形,产生了NNW逆向剪切带和NEE走滑剪切带,这时含铁岩系中形成平行韧性剪切带的片理S_2。2000Ma发生第三幕韧性变形,其中NEE和NNW向剪切性质与第二幕恰好相反。以上三幕韧性剪切序次,相对应的形成了片麻岩、糜棱岩和构造片岩。

       

      Abstract: The Archean crust in the Anshan area is composed mainly of two metamorphic rockseries, i.e. granitic rocks (making up about 90%) and supracrustal rocks (i. e. iron-bearing rock series).Granite may be subdivided into the Tiejiashan granite and the Gongchangling granite, while thesupracurstal rocks are composed of itabirite and sericite -chlorite -quartz schist.The supracrustal rocks were deposited over 3000 Ma ago and the Tiejiashan granite was em-placed 2900 Ma ago. The first phase of ductile deformation took place slightly later. NE gneis-sosity occurred in the Tiejiashan granite, whereas homoclines with a NE axial direction and axialplane schistosity S1 were formed in supracrustal rocks. The Gongchangling granite was emplacedabout 2600 Ma ago and slightly later the second phase of ductile deformation happened, givingrise to NNW reverse shear zones and ENE strike -slip shear zones and producing schistosity S2 ofparallel ductile shear zones in iron -bearing rock series The third phase of ductile deformationtook place 2000 Ma ago. The characters of ENE and NNW shear zones formed in this phase arecontrary to those of the second phase. The deformation of ductile shear zones of the above-men-tioned ductile shear zones formed successively gneiss, mylonite and tectonic schist that correspondto the three phases.

       

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