祁连山地区镁铁——超镁铁岩的多样性

祁连山地区出露有不同类型的镁铁－超镁铁岩，包括蛇绿岩，阿拉斯加型岩体，橄榄岩－闪长岩型岩体以有产于北祁连西部的一种特殊的镁铁－超镁铁岩组合。不同的镁铁－超镁铁岩形成于一同的构造环境，蛇绿岩代表洋壳的残片，阿拉斯加型岩体产生岛弧或活动陆缘环境，橄榄岩一闪长岩体则是板块碰撞之后形成的，根据蛇绿岩与大致同时代的阿拉斯加型岩体产出的位置，推测在北祁连早古生代时存在向南的消减事件。

THE DIVERSITY OF MAFIC-ULTRAMAFIC ROCKS IN QILIAN MOUNTAINS

There are distinct types of mafic ultramafic rocks in Qilian Mountains, including ophiolite, Alaskan type body, peridotite diorite type body, and probably a new type of mafic ultramafic rock which was previously unknown and is seen only in western part of Qilian Mts. It is possible that different mafic ultramafic rock would be formed in different settings: ophiolite was a relic of oceanic lithosphere, Alaskan type body was probably formed in island arc or active continental margin settings, and peridotite diorite type body was intruded in post collision stage. It is inferred that the Qilian oceanic basin was subducted towards south during Early Paleozoic by the distribution of the Yushigou ophiolite and the Zamashigou Alaskan type body. The Laohushan peridotite diorite type body which was intruded during Middle Late Silurian period, formed in within plate settings of post collision stage, has island arc characteristics geochemically. We try to illustrate them with double influences of magma sources and continental contamination. The mafic ultramafic assemblage from the Qiqing area may be a new kind of mafic ultramafic rock related to continental extension.