柴达木北缘大型韧性剪切带构造特征

柴达木北缘韧性剪切带发育于元古界达肯大坂群中深变质岩以及上奥陶统浅变质火山岩中,属中角度逆冲型韧性剪切带,形成于地壳中深层次,与加里东末期柴达木板块由南向北下插到祁连板块之下,以及祁连板块自北向南的仰冲—即祁连、柴达木板块的陆陆碰撞作用有直接的成因联系。该韧性剪切带为本次研究工作中首次发现,对于其构造特征的研究和厘定,将有助于柴达木北缘大地构造环境及变质变形历史的深入研究。

Tectonic Characteristics of the Ductile Shear Zone on the North Margin of Qaidam Basin, Qinghai Province

The ductile shear zone on the north margin of Qaidam basin is discovered firstly. It developed in the medium-high grade metamorphic rocks of Proterozoic group and lowgrade metamorphic volcanic rocks of Ordovician system. It belongs to a obduction-type ductile shear zone. Its formation was related to the collision between the Qilian and Qaidam continents. In late Caledonian period, the Qaidam ancient ocean lo- cated on the north of the Qaidam plate began to closure. The ocean crust subducted under the Qilian plate, finally the ocean disappeared. Then, the Qaidam plate subducted under the Qilian plate. And, of course, the Qilian plate obducted on the Qaidam plate. The ductile' shear zone on the north margin of Qaidam basin was formed during the collision process of those both continents. The discovery of this ductile shear zone is very important for us to recognize the tectonic environment of Qaidam and Qilian area.