北祁连东部两类Ⅰ型花岗岩定年及其地质意义

Dating of two types of granite from north Qilian, China

北祁连东部早古生代地层中产出两种特征不同的I型花岗岩类,其一以井子川岩体为代表,暗色矿物以角闪石为主,稀土总量为90×10^(-6)～106×10^(-6),轻重稀土比值小于8,锆石的SHRIMP年龄为464±15Ma,岩体形成的构造环境类似于岛弧;其二是以黄羊河岩体为代表,暗色矿物以黑云母为主,稀土总量为214×10^(-6)～250×10^(-6),轻重稀土比值大于8,锆石的LA-ICP-MS年龄为383±6 Ma,岩体形成于碰撞后环境。

Two types of granite with different characters occurred in strata of the lower Paleozoic. One is a representation of Jingzichuan rock body, which is characterized by dark mineral hornblende, the REE total 90 x 10(-6) similar to 106 x 10(-6) and the ratio of LREE/HREE to be less than 8 (ranged from 6.9 to 7.8) and having zircon SHRIMP age of 464 +/- 15Ma, tectonically, intruded in island arc environment. The other is the Huangyanghe rock body, which by dark mineral biotite, the REE total of 214 x 10(-6) similar to 250 x 10(-6), the ratio of LREE/HREE to be more than 8 (ranged from 8.2 to 9.7) having zircon LA-ICP-MS age of 383 +/- 6Ma, tectonically, intruded in post-collisional stage.