伊春地区青岭经营所晚二叠世花岗岩的发现及地质意义

伊春市青岭经营所花岗岩具有高硅、富碱和过铝质特点,稀土元素配分模式以轻稀土元素富集且缓向右倾斜、重稀土元素较为平坦、铕略亏损-弱正异常型式,微量元素大离子亲石元素Ba、K、Sr显示为负异常,高场强元素Hf、Zr为正异常,P、Ti、Nb为负异常,岩石地球化学显示S型花岗岩特点。R1-R2图解中样品落入造山晚期,具后碰撞花岗岩特征。中细粒花岗闪长岩锆石U-Pb同位素测年206Pb/238U加权平均年龄为258±3 Ma,细中粒二长花岗岩两个样品锆石206Pb/238U加权平均年龄分别为261±1 Ma、267.3±1.4 Ma,三个样品测年表明花岗岩形成于晚二叠世。该花岗岩的锆石U-Pb年龄的确定和成因的探讨对于深入研究伊春地区晚古生代构造岩浆演化具有十分重要的意义。

Discovery and Geological Significant of the Late Permian Granite in Qingling Jingyingsuo Area,Yichun

Qingling Jingyingsuo grantie in Yichun region is characterized by high slica,high alkali,and peralumi-nous grantie.The corordrite-normalized rare earth element(REE)pattern shows light rare earth elements(LREE) enrichment, with a slightly right oblique LREE pattern and a realtive flat HREE one,which constitues a weak pos-itive anomaly curve with Eu nagtive anomaly. Large ion lithophile elements(LILE) such as Ba、K、Sr and P、Ti、Nb show nagtively anomaly while high-field strengh elements such as Hf and Zr show positive anomaly. Litho-geochemical features indicate S type granite, the R1-R2 diagram shows the granite formed in the tectonic environ-ment of late orogenic epoch which has the characteristic of post-tectonic granite.The weighted mean 206Pb/238U age of zircon from medium-fine granodiorite is about 258 ± 3 Ma.The respective weighted mean 206Pb/238U age of zir-con from the two samples of fine-medium monzonitic granite is 267.1 ± 1.4 Ma and 267.3 ± 1.4 Ma, the result shows the grantie formed in Permian Epoch. The U-Pb isotopic age of zircon and the origin of the grantie are of significance for further study of late Paleozoic tectonic and magmatic evolution in Yichun.