柴达木北缘奥陶纪火山作用与构造机制

柴达木北缘奥陶系海相火山岩（洋脊及洋岛火山岩组合）是柴北缘奥陶纪古洋盆存在的重要证据。奥陶纪末期，柴北缘洋盆逐渐闭合，洋壳自南向北下插到祁连陆块之下。大洋消失后，俯冲作用携带柴达木陆块继续下插，祁连陆块则自北向南道冲到柴达木陆块之上，柴北缘成为陆－陆碰撞型造山带。从而在柴达木北缘地区，自北而南形成了祁连超叠壳楔、柴北缘碰撞混杂岩带以及柴达木俯冲壳楔的三单元结构模式。

VOLCANISM AND TECTONIC SETTING DURING ORDOVICIAN PERIOD ON NORTH MARGIN OF QAIDAM

There are three main petrotectonic assemblages on north margin of Qaidam-mid-ocean ridge volcanic rock assemblage (tholeiite series),ocean island (seamount) volcanic rock assemblage (alkaline series),and island arc volcanic rock assemblage (cafe-alkaline and tholeiite series). They are of geochemistry features of tectonic melange.Last stage of Ordovician,the ocean basin on north margin of Qaidam closed gradually,then Qaidam continental block subducted continually and Qilian continental block thrusted onto Qaidam continental block in the direction from north to south, formed the orogenic belt of continent-continent collosion type.As a result,the three unit model formed, which consisted of Qilian overlying crustal wedge, the collosion tectonic melange belt on north margin of Qaidam and Qaidam underthrusted wedge.