北祁连东段米家山地区碰撞变质作用研究

:米家山地区位于北祁连东段 ,区内下奥陶统阴沟群为一套海相火山—碎屑岩建造。在加里东末期 ,米家山岩体最终定位。通过填图发现 ,岩体与阴沟群变质地层呈“互层状”产出。在岩体的中心部位发育两条角闪岩相变质带 ,其变质条件由早期中—高压中温向晚期低压高温演化 ,变质作用为多期碰撞变质作用。这一现象不仅反映了造山作用是一个连续过程 ,同时也说明了与其相伴的变质作用必然是一个变化的过程。在与花岗岩相伴的地区 ,严格地用区域变质作用和接触变质作用来解释变质成因是与板块构造观点不相符合的 ,它们可能是一个起因的不同结果 ,是相互联系的

RESEARCH ON COLLISION METAMORPHISM IN MIJIASHAN AREA IN THE EASTEN PART OF NORTH QILIAN TECTONIC BELT

Mijiashan area is located in the eastern part of North Qilian tectonic belt.Yingou Group of Early Ordovician consists of marine volcanic sedimentary association. At the end of Caledonian, Mijiashan granite pluton was formed. Based on regional mapping, it is found that the granite and the metamorphic rocks are distributed in the manner of interbeds. In the center of the pluton, there exist two amphibolite facies metamorphic zones, and their metamorphic conditions were evolved from medium-high pressure to low pressure. The metamorphism is attributed to multi collisions.This phenomena not only indicates that the orogenesis is a continuous process,but also demonstrates that the metamorphism related to the orogenesis is a changing process.In the metamorphic area in which granites occur,it is incompatible to plate tectonic theory to interpret the metamorphic mechanism by regional or contact metamorphism.They belong to different results resulting from one cause and related to each other.