祁连山东南段加里东造山期构造变形年代的精确限定及其意义  

Precise Timing and Significance of Caledonian Structural Deformation Chronology in Southeast Qilian

作　　者：樊光明[1] 雷东宁[1] 

机构地区：[1]中国地质大学地球科学学院,湖北武汉430074

出　　处：《地球科学（中国地质大学学报）》2007年第1期39-44,共6页Earth Science-Journal of China University of Geosciences

基　　金：中国地质调查局基金项目(Nos200213000016;200413000007)

摘　　要：祁连山东南段呈北西-南东向展布着加里东期中祁连造山带和拉脊山造山带，其基底为前加里东变质岩系，在该变质结晶基底岩系中发育着菱形网格状韧性剪切带，共轭韧性剪切带面对缩短方向的夹角为104°～114°，其最大主应力方位为SW210°左右．在中祁连地块金沙峡和化隆地块科却两处韧性剪切带中的糜棱岩化岩石，获取变质矿物白云母40^Ar-39^Ar坪年龄分别为（405．1±2．4）Ma和（418．3±2．8）Ma．这一年代学结果不仅确定了加里东基底变质岩系中韧性剪切带是加里东造山作用过程中形成，更重要的是通过对基底韧性剪切带中变质变形岩石的年代学研究，精确地限定了祁连山东南段的早古生代火山盆地（或岛弧盆地）、拉脊山小洋盆关闭的构造年代．这为造山带构造演化过程中盆地关闭时间的确定开辟了新的途径．The middle Qilian orogenic belt and Lajishan orogenic belt of the Caledonian strike NW-SE direction in the southeast Qilian and its basement consists of Pre-Caledonian metamorphic rock series. The lozenge-cancellate-shaped ductile shear zone occurs in the crystalline basement, and the included angle of shortening direction of conjugated ductile shear zones ranges from 104° to 114° and the max principal stress direction indicates approximate SW210°. The 40 ^Ar39 ^Ar plateau ages of muscovite obtained from the mylonitilization rock in ductile shear zone of Jinshaxia within middle Qilian massif and Keque in Hualong massif are （405. 1±2.4）Ma and （418. 3±2. 8）Ma, respectively. The chronology data determine the ductile shear zones in Caledonian basement metamorphic rock formed through the Caledonian orogeny. Furthermore, the chronological study of basement rock determines precise forming period for the close of the Late Paleozoic volcanic basin （or island-arc ba sin） and Lajishan ocean basin. This offers a new approach to the determination of ocean basin closing time in the process of structural evolution of orogenic belt.

关 键 词：祁连山东南段 加里东造山带 韧性剪切带 变质变形事件 构造-热年代学 

分 类 号：P597[天文地球—地球化学] P542[天文地球—地质学]